The prevalence of headache may be related with the latitude: a possible role of Vitamin D insufficiency?
© Springer-Verlag 2010
Received: 21 March 2010
Accepted: 26 April 2010
Published: 13 May 2010
According to recent observations, there is worldwide vitamin D insufficiency (VDI) in various populations. A number of observations suggest a link between low serum levels of vitamin D and higher incidence of chronic pain. A few case reports have shown a beneficial effect of vitamin D therapy in patients with headache disorders. Serum vitamin D level shows a strong correlation with the latitude. Here, we review the literature to delineate a relation of prevalence rate of headaches with the latitude. We noted a significant relation between the prevalence of both tension-type headache and migraine with the latitude. There was a tendency for headache prevalence to increase with increasing latitude. The relation was more obvious for the lifetime prevalence for both migraine and tension-type headache. One year prevalence for migraine was also higher at higher latitude. There were limited studies on the seasonal variation of headache disorders. However, available data indicate increased frequency of headache attacks in autumn–winter and least attacks in summer. This profile of headache matches with the seasonal variations of serum vitamin D levels. The presence of vitamin D receptor, 1α-hydroxylase and vitamin D-binding protein in the hypothalamus further suggest a role of vitamin D deficiency in the generation of head pain.
KeywordsVitamin D Headache Migraine Tension-type headache Pain Chronic daily headache Vitamin D receptor
The prevalence and incidence of headache differ widely between countries and there is an intriguing geographical pattern . Several factors can be responsible for the differences of prevalence between countries, such as methodological differences in the studies, and cultural, environmental, metabolic and genetic factors, etc.
Vitamin D insufficiency (VDI) has emerged as a widespread global public health issue in the recent times. Rickets and osteomalacia are the most common manifestations of VDI. However, recent observations and hypotheses suggest that VDI may affect almost every system of the body . A number of observations have suggested an association between low serum levels of vitamin D and higher incidence of chronic pain . Anecdotal evidences suggest that vitamin D may be effective in a few headache disorders [4–6]. If the prevalence rate of a particular disease increases with increasing latitude, vitamin D deficiency is another possibility. The role of vitamin D in the pathogenesis of a few disorders was purported only when it was noticed that the prevalence of the disease has some relation with latitude.
We review the articles reporting a role of vitamin D in headache disorders. We also review the literature to delineate a relation of prevalence rate of headaches with the latitude.
Review of literature
A number of recent observations, including small randomized controlled trials, suggest a link between low serum levels of vitamin D and higher incidence of chronic pain . There is no consensus on the optimal levels of vitamin D. 25-Hydroxyvitamin D level (25(OH) D) of more than 30 ng/ml is usually considered as a sufficient vitamin D level. Vitamin D deficiency is considered when serum 25 (OH) D level is less than 20 ng/ml. Between 20 and 30 ng/ml of 25 (OH) D levels indicate a VDI state . Observations of vitamin D levels with painful conditions have been made on musculoskeletal pain of limbs, trunk and joints. No such study has been done in patients with headache. There are just a few case reports or observations suggesting a role of vitamin D in headaches [4–6]. Recently, Turner et al.  studied the prevalence of vitamin D inadequacy (<20 ng/ml) among 267 patients with chronic pain, including headache (25 patients). The prevalence of VDI among these 267 patients was 26%. However, the details of vitamin D levels in headache patients were not provided. The first case report on a role of vitamin D (with calcium supplementation) was probably reported by Thys-Jacobs  in 1994. The author demonstrated the beneficial effect of vitamin D in two female patients with a history of menstrually related migraine and premenstrual syndrome. Both the patients had low serum vitamin D levels (case 1: less than 5 ng/ml; case 2: 17 ng/ml). Both patients received vitamin D (1,200–1,600 IU daily) and calcium (1,200–1,600 mg daily) supplementation. There was a significant reduction in migraine attacks in 2–3 months. Later on, the same author  showed dramatic reduction in the frequency and duration of migraine headaches in another two postmenopausal migraineurs with vitamin D and calcium supplementation. The serum 25 (OH) D levels in these two patients were 19.8 ng/ml (Case 1) and 15 ng/ml (Case 2). Wheeler  studied the serum vitamin D levels in chronic migraine patients; 14.8% of patients had levels of ≤20 ng/ml and another 25.9% of patients had levels between 20 and 30 ng/ml. Recently, Prakash and Shah  reported eight patients with vitamin D insufficiency having symptoms of both osteomalacia and chronic tension-type headache. All patients had vitamin D levels of ≤10 ng/ml. Both headache and osteomalacia responded to vitamin D and calcium supplementation in a few weeks’ duration. Vitamin D insufficiency constitutes an unrecognized epidemic in many populations worldwide. Therefore, the causal association of any disease with vitamin D insufficiency or deficiency should be judged cautiously.
If vitamin D is important in the generation of head pain, the incidence of headache will be higher at higher latitudes. There is at least one report on the relation of headache prevalence with latitude. Mitsikostas et al.  studied the prevalence of headache in Greece and noted a correlation of the frequency of daily headache with latitude. The prevalence and frequency of daily headache was higher in the northern regions (higher latitude) than in southern areas. We further searched the literature for a possible relation of headache prevalence with the latitude. Search methods included MEDLINE, review articles and reference lists of relevant manuscripts. The MEDLINE search was conducted using the keywords “headache”, “prevalence” and “epidemiology”. Studies were included if they were: (1) population based; (2) conducted in the general populations; (3) reporting lifetime or 1-year prevalence of total headaches, migrainous headaches and tension headaches; (4) studies using IHS classification or published after 1988; (5) studies conducted in a city or small county/provinces or small countries with a narrow latitudinal range (up to 5°). Articles were excluded if (1) the studies were not conducted on the general population (e.g., among students, clinic-based studies, in workplaces, only in a limited age group and only on one gender); (2) studies not describing the time frame for determination of prevalence rate; (3) national population survey done in a country with a wide latitudinal range (more than 5°, such as the USA, Canada, Brazil, Japan, France, Sweden, Germany, Denmark); (4) studies on rare types of headache disorders.
We looked for a relation of headache prevalence with latitude. The latitude of the city or country, described in the manuscript, was determined by “Google Earth”. The mean latitude of the country was used as a reference for seeking its relation with headache prevalence in small countries.
Although every effort was taken to include all the relevant data described in literature, it might be possible that some important data could have been missed. We faced a few problems in including the studies. There were many differences in methodology and reporting patterns among the studies. A few studies explored/reported the same population on two or more occasions. Time frame for determining the prevalence rate was not described in a few observations. Some articles described the prevalence rates in males and females separately, but failed to give a combined (male and female together) prevalence rate. On a few occasions, we calculated the combined prevalence rate. For calculating the total headache prevalence, we combined the total number of male and female patients (if number was given in the article) having headache and then expressed it in percentage (the usual method of determining headache prevalence). The headache types/subclassifications were not very clear in some studies (such as non-migrainous headaches, mixed headaches, etc.). We excluded such type of studies from the final review to minimize the confounding factors.
Both lifetime and 1-year prevalence for the total headaches did not show any significant relation with the latitude (and we did not include total headache prevalence in the table). However, we noted two studies with very low prevalence of total headache near equatorial areas. Both studies did not define the time frame for the headache prevalence. Gourie-Devi et al.  reported prevalence of various neurological disorders in Bangalore, India (12°N). Their survey recruited 102,557 subjects. Prevalence rate for headache was only 1.1%. Similarly, the prevalence of headache was relatively low (4%) in Hong Kong (22°N), in the screening of 7,356 persons . These prevalence rates are very low even if we consider these two as point prevalence.
The prevalence of tension headache and migraine (arranged in ascending order of latitude)
One year prevalence
Ho et al. (2003) 
San Pablo del Lago (Ecuador)
Cruz et al. (1995) 
Mbulu, Manyara, Tanzania (Africa)
Gbêcon-Hounli, Abomey, Benin (Africa)
Houinato et al. (2010) 
Tekle haimont et al. (1995) 
Osuntokun et al. (1992) 
Nachingwea (Tanzania) (Africa)
Dent et al. (2004) 
Jaillord et al. (1997) 
Miranda et al. (2003) 
Cheung (2000) 
Eastern province (Thugabah) (Saudi Arabia)
Al Rajeh et al. (1997) 
Ad Dakhliyah (Oman)
Delu et al. (2002) 
Wang et al. (2000) 
Qassim (Saudi Arabia)
Abduljabbar et al. (1996) 
Porto Alegre (Brazil)
Wiehe et al. (2002) 
Alzoubi et al. (2009) 
Takeshima et al. (2003) 
Roh et al. (1998) 
Baltimore, Atlanta, and Philadelphia (USA)
Bigal et al. (2006) 
Stewart et al. (1996) 
Lipton et al. (2002) 
Kececi et al. (2002) 
Celik et al. (2005) 
Tbilisi and Kakheti (Georgia)
Katsarava et al. (2009) 
Doetinchem & Maastricht (Netherlands)
Launer et al. (1999) 
Steiner et al. (2003) 
Rasmussen et al. (1991) 
Akershus, Hedmark or Oppland (Norway)
Russell et al.  
Hagen et al. (2000) 
Lilleng et al. (2009) 
A total of about 50 publications relevant to 1-year prevalence were identified. Studies on populations of less than 1,000 were excluded for the observations. Finally, 22 studies were included for the observations (Table 1). The relation of 1-year prevalence rate with latitude was not as strong as that observed with lifetime prevalence rate. However, there were some suggestions indicating that prevalence of headache would be higher at higher latitude. We noted 11 studies relevant to 1-year migraine prevalence in the cities or provinces situated between 0° and 35° (N or S). The prevalence rate was 3.0–13.5. Prevalence rate of more than 10 was noted only in two studies. The maximum 1-year prevalence rate was 13.5 below 35° latitude. There were 11 studies at latitudes higher than 35°. The prevalence ranged from 11.6 to 22.3%. None of the studies had prevalence rates less than 10. We found only nine population-based studies on tension-type headaches reporting a 1-year prevalence rate. Most of the studies were conducted on subjects residing between 22° and 41° of latitude. Six of these studies reported a 1-year prevalence rate of more than 25%. There is only one study outside this range (at 3°N) (Table 1). Because of the limited number of studies, we could not draw on any conclusion. However, a study done in Tanzania (3°S)  on 7,412 person demonstrated a very low 1-year prevalence rate (7%), and this may further support a possibility of low prevalence rate at the equatorial area (as noted above with lifetime prevalence rate for tension-type headache). We observed 16 studies on the 1-year prevalence of chronic daily headaches. However, because of the low prevalence rate, no conclusion or suggestions could be made.
We also tried to look at nationwise surveys of big countries that described the details of regional prevalence (especially, details of northern and southern areas). However, there were only a few studies with details of regional prevalence. Queiroz et al.  did an observational, cross-sectional population-based study for TTH in the 26 states of Brazil. They reported regionwise prevalence. Brazil is a very big country with a wide range of latitudes. Therefore, we should be very cautious in interpreting the data in relation to the latitudes. Nevertheless, the prevalence rate in southern Brazil (higher latitude) (14.1%) was more than two times that of northern Brazil (6.8%). However, this trend of prevalence was not corroborated in the same population for chronic daily headache. The prevalence of CDH was 6.0% in the south and 10.2% in the north .
Serum vitamin D levels vary with the season. It peaks in the months of May–September. The levels tend to be lower from November to March [51–53]. If vitamin D has any association with headache, the prevalence rate of headache should match with the usual seasonal variation of vitamin D levels. Sudden weather change is one of the most important factors for the attacks of headache (especially migraine). Bright sunlight exposure is another important factor for precipitating headache attacks [53, 54]. Therefore, it will be very difficult to comment on actual circannual or seasonal variations on headache prevalence.
Most of the studies on season and headache look for the effects of weather variables (such as temperature, rain, humidity, atmospheric changes, etc.) in precipitating headache attacks [53, 54]. Soriani et al.  studied the seasonal variation of migraine attacks in children and noted increased frequency of attacks in autumn–winter (especially November–January) with a minimum frequency in July. A circannual variation with a peak in January has also been reported for migraine in adults. . Marrelli et al.  studied the seasonal and meteorological factors in primary headache disorders. The overall frequency of headaches was highest during winter and least in summer: 17.9% perceived more headaches in winter, 14.9% in spring, 11.5% in autumn and 10.6% in summer. Limited studies on this issue have prevented us from giving any comments with confidence. However, increased frequency of attacks in autumn–winter (October–January) and least attacks in summer indirectly suggest a role for VDI in the generation of recurrent headaches.
The prevalence rates of a number of diseases increase with increasing latitude, i.e., prevalence rates tended to be very low near the equator and to increase as one moved toward the poles. Duration and intensity of sunlight shows a strong correlation with latitude (hence serum vitamin D level). The protective effect of vitamin D (or sunlight) in reducing the risk of cancer mortality rate was first suggested when Garland and Garland  noted that colon cancer mortality rates were highest in places where populations were exposed to the least amounts of natural light: major cities and rural areas in high latitudes. This ecological approach was used to find the first link between vitamin D insufficiency (minimal sun exposure) and increased risk for other carcinomas (breast and ovarian carcinoma) . As the prevalence rate of headache is probably related with the latitude, a link between VDI and increased prevalence rate of headache disorders exist.
Low average income, illiteracy and poor health care facilities are considered as risk factors for various diseases. Also, the prevalence rate of headache has been demonstrated to be higher in the illiterate (or with low education level) population, population with low income and with poor healthcare facilities, etc. . Average income, literacy and health-care facilities are poorer across the equator. Therefore, a high prevalence of headache should be suspected in these areas. However, we noted low prevalence in these areas. Therefore, we suspect the presence of some protective factors at the lower latitude areas. As higher serum vitamin D levels are found in the population living at a lower latitude, it may be one of the important factors for the low prevalence. However, our observations (a positive relation of headache prevalence with latitude) should be judged very cautiously. At the present, it will be difficult to determine whether these observations are real or due to methodological differences in the studies. Genetic predisposition or racial differences are other factors to be considered in this discussion, although the prevalence of VDI also depends on genetic and racial factors . The levels of vitamin D vary during the year. Therefore, the incidence or frequency of any disease causally related with VDI will vary with the timing of the studies. Although lifetime or 1-year prevalence of headache will not be affected much by the timing of the studies, we should be cautious in interpreting such data as recall bias may vary with timing: people tend to remember their more recent headaches. Besides latitude and season, many other factors affect the serum vitamin D levels. People who avoid sunlight, at any latitude, are at risk of vitamin D deficiency. Dark skin pigmentation, use of sunscreen, clothing, air pollution, cloud cover, etc., are other factors that affect the vitamin D status of a person or the population . However, despite all these barriers, people may have normal serum vitamin D levels if they take adequate oral vitamin D, including the use of over-the-counter prescriptions. The analytical problems in relation to vitamin D assays are other points to be considered before deciding a causal association of any disease with vitamin D deficiency . Therefore, our observations should be judged very cautiously, as the possibility of many confounding factors exist.
It is difficult to speculate on the exact role of vitamin D in the generation of head pain, as the pathogenesis of even bone and muscle pain in patients with VDI is still being determined. Recently, the presence of VDR and 1α-hydroxylase (1α-OHase), the enzyme responsible for the formation of the active vitamin, have been demonstrated in many areas of the central nervous system including the prefrontal cortex, hippocampus, cingulate gyrus, thalamus and hypothalamus . Eyles et al.  studied the distribution of VDR and 1α-hydroxylase in the brain. The strongest immunohistochemical staining for both the receptor and enzyme was noted in the hypothalamus (and substantia nigra.). Recently, Jirikowski et al.  studied immunostaining for vitamin D-binding protein (DBP) in rat hypothalamus. DBP was observed in widespread axonal projections throughout the lateral hypothalamus .
The exact functions of this VDR in the various sites of the brain are yet to be determined. However, the presence of VDR and 1α-hydroxylase in the areas (especially hypothalamus) implicated in the pathophysiology of various primary headache disorders suggests that VDI may have a role in the generation (or precipitation) of head pain.
In conclusion, increased incidence of headache prevalence at higher latitudes hints at a role of VDI in the pathogenesis of headache disorders. Demonstration of vitamin D receptor, 1α-hydroxylase, and vitamin D-binding protein in the hypothalamus further supports a role of vitamin D deficiency in the generation of head pain. We hope our review will act as a catalyst for a controlled study to clarify the issue.
No grant or support for this study was provided.
Conflict of interest
- Stovner Lj, Hagen K, Jensen R, Katsarava Z, Lipton R, Scher A et al (2007) The global burden of headache: a documentation of headache prevalence and disability worldwide. Cephalalgia 27(3):193–210, 10.1111/j.1468-2982.2007.01288.x, 17381554View ArticlePubMedGoogle Scholar
- Holick MF (2007) Vitamin D deficiency. N Engl J Med 357:266–281, 10.1056/NEJMra070553, 17634462, 1:CAS:528:DC%2BD2sXotVejsbc%3DView ArticlePubMedGoogle Scholar
- Straube S, Andrew Moore R, Derry S, McQuay HJ (2009) Vitamin D and chronic pain. Pain 141(1–2):10–13, 10.1016/j.pain.2008.11.010, 19084336, 1:CAS:528:DC%2BD1MXjvFSrug%3D%3DView ArticlePubMedGoogle Scholar
- Prakash S, Shah ND (2009) Chronic tension-type headache with vitamin D deficiency: casual or causal association? Headache 49(8):1214–1222, 10.1111/j.1526-4610.2009.01483.x, 19619241View ArticlePubMedGoogle Scholar
- Thys-Jacobs S (1994) Vitamin D and calcium in menstrual migraine. Headache 34(9):544–546, 10.1111/j.1526-4610.1994.hed3409544.x, 8002332, 1:STN:280:DyaK2M%2FpsFKgtA%3D%3DView ArticlePubMedGoogle Scholar
- Thys-Jacobs S (1994) Alleviation of migraines with therapeutic Vitamin D and calcium. Headache 34:590–592, 10.1111/j.1526-4610.1994.hed3410590.x, 7843955, 1:STN:280:DyaK2M7ks1ehtQ%3D%3DView ArticlePubMedGoogle Scholar
- Turner MK, Hooten WM, Schmidt JE, Kerkvliet JL, Townsend CO, Bruce BK (2008) Prevalence and clinical correlates of vitamin D inadequacy among patients with chronic pain. Pain Med 9(8):979–984, 10.1111/j.1526-4637.2008.00415.x, 18346069View ArticlePubMedGoogle Scholar
- Wheeler SD (2008) Vitamin D deficiency in chronic migraine. Headache 48(S1):S52–S53Google Scholar
- Mitsikostas DD, Tsaklakidou D, Athanasiadis N, Thomas A (1996) The prevalence of headache in Greece: correlations to latitude and climatological factors. Headache 36(3):168–173, 10.1046/j.1526-4610.1996.3603168.x, 8984090, 1:STN:280:DyaK2s7gsVyhsw%3D%3DView ArticlePubMedGoogle Scholar
- Ho KH, Ong BK (2003) A community-based study of headache diagnosis and prevalence in Singapore. Cephalalgia 23:6–13, 10.1046/j.1468-2982.2003.00272.x, 12534573View ArticlePubMedGoogle Scholar
- Cruz ME, Cruz I, Preux PM, Schantz P, Dumas M (1995) Headache and cysticercosis in Ecuador, South America. Headache 35(2):93–97, 10.1111/j.1526-4610.1995.hed3502093.x, 7737869, 1:STN:280:DyaK2M3ls1SmtQ%3D%3DView ArticlePubMedGoogle Scholar
- Winkler A, Stelzhammer B, Kerschbaumsteiner K, Meindl M, Dent W, Kaaya J, Matuja W, Schmutzhard E (2009) The prevalence of headache with emphasis on tension-type headache in rural Tanzania: a community-based study. Cephalalgia 29(12):1317–1325, 10.1111/j.1468-2982.2009.01885.x, 19438921View ArticlePubMedGoogle Scholar
- Winkler A, Dent W, Stelzhammer B, Kerschbaumsteiner K, Meindl M, Kaaya J, Matuja W, Schmutzhard E (2009) Prevalence of migraine headache in a rural area of northern Tanzania: a community-based door-to-door survey. Cephalalgia. doi:10.1111/j.1468-2982.2009.01994.x
- Houinato D, Adoukonou T, Ntsiba F, Adjien C, Avode DG, Preux PM (2010) Prevalence of migraine in a rural community in south Benin. Cephalalgia 30:62–67PubMedGoogle Scholar
- Tekle Haimanot R, Seraw B, Forsgren L, Ekbom K, Ekstedt J (1995) Migraine, chronic tension-type headache, and cluster headache in an Ethiopian rural community. Cephalalgia 15(6):482–488, 10.1046/j.1468-2982.1995.1506482.x, 8706111, 1:STN:280:DyaK28zhsl2quw%3D%3DView ArticlePubMedGoogle Scholar
- Osuntokun BO, Adeuja AO, Nottidge VA, Bademosi O, Alumide AO, Ige O, Yaria F, Schoenberg BS, Bolis CL (1992) Prevalence of headache and migrainous headache in Nigerian Africans: a community-based study. East Afr Med J 69(4):196–199, 1644029, 1:STN:280:DyaK38zlsVGgsQ%3D%3DPubMedGoogle Scholar
- Dent W, Spiss H, Helbok R, Matuja W, Scheunemann S, Schmutzhard E (2004) Prevalence of migraine in a rural area in South Tanzania: a door-to-door survey. Cephalalgia 24(11):960–966, 10.1111/j.1468-2982.2004.00775.x, 15482359, 1:STN:280:DC%2BD2crht1Chsw%3D%3DView ArticlePubMedGoogle Scholar
- Jaillard AS, Mazetti P, Kala E (1997) Prevalence of migraine and headache in a high-altitude town of Peru: a population-based study. Headache 37(2):95–101, 10.1046/j.1526-4610.1997.3702095.x, 9074294, 1:STN:280:DyaK2s3ivVaitA%3D%3DView ArticlePubMedGoogle Scholar
- Miranda H, Ortiz G, Figueroa S, Pena D, Guzman J (2003) Prevalence of headache in Puerto Rico. Headache 43(7):774–778, 10.1046/j.1526-4610.2003.03135.x, 12890132View ArticlePubMedGoogle Scholar
- Cheung RT (2000) Prevalence of migraine, tension-type headache, and other headaches in Hong Kong. Headache 40(6):473–479, 10.1046/j.1526-4610.2000.00071.x, 10849044, 1:STN:280:DC%2BD3cvht1Oruw%3D%3DView ArticlePubMedGoogle Scholar
- Al Rajeh S (1997) The prevalence of migraine and tension headache in Saudi Community; a community based study. Eur J Neurol 4:502–506View ArticleGoogle Scholar
- Deleu D, Khan MA, Al Shehab TA (2002) Prevalence and clinical characteristics of headache in a rural community in Oman. Headache 42(10):963–973, 10.1046/j.1526-4610.2002.02225.x, 12453027View ArticlePubMedGoogle Scholar
- Wang SJ, Fuh JL, Young YH, Lu SR, Shia BC (2000) Prevalence of migraine in Taipei, Taiwan: a population-based survey. Cephalalgia 20(6):566–572, 10.1046/j.1468-2982.2000.00085.x, 11075840, 1:STN:280:DC%2BD3M7ktFGntg%3D%3DView ArticlePubMedGoogle Scholar
- Abduljabbar M, Ogunniyi A, Al Balla S, Alballaa S, Al-Dalaan A (1996) Prevalence of primary headache syndrome in adults in the Qassim region of Saudi Arabia. Headache 36(6):385–388, 10.1046/j.1526-4610.1996.3606385.x, 8707558, 1:STN:280:DyaK28zitFCrsA%3D%3DView ArticlePubMedGoogle Scholar
- Wiehe M, Fuchs SC, Moreira LB, Moraes RS, Fuchs FD (2002) Migraine is more frequent in individuals with optimal and normal blood pressure: a population-based study. J Hypertens 20(7):1303–1306, 10.1097/00004872-200207000-00016, 12131526, 1:CAS:528:DC%2BD38Xlt1Kmt7w%3DView ArticlePubMedGoogle Scholar
- Alzoubi KH, Mhaidat N, Azzam SA, Khader Y, Salem S, Issaifan H, Haddadin R (2009) Prevalence of migraine and tension-type headache among adults in Jordan. J Headache Pain 10(4):265–270, 10.1007/s10194-009-0122-6, 19387792PubMed CentralView ArticlePubMedGoogle Scholar
- Lavados PM, Tenhamm E (1997) Epidemiology of migraine headache in Santiago, Chile: a prevalence study. Cephalalgia 17(7):770–777, 10.1046/j.1468-2982.1997.1707770.x, 9399008, 1:STN:280:DyaK1c%2FmtFemug%3D%3DView ArticlePubMedGoogle Scholar
- Lavados PM, Tenhamm E (1998) Epidemiology of tension-type headache in Santiago, Chile: a prevalence study. Cephalalgia 18(8):552–558, 10.1046/j.1468-2982.1998.1808552.x, 9827247, 1:STN:280:DyaK1M%2FksVCqtA%3D%3DView ArticlePubMedGoogle Scholar
- Takeshima T, Ishizaki K, Fukuhara Y, Ijiri T, Kusumi M, Wakutani Y, Mori M, Kawashima M, Kowa H, Adachi Y, Urakami K, Nakashima K (2004) Population-based door-to-door survey of migraine in Japan: the Daisen study. Headache 44(1):8–19, 10.1111/j.1526-4610.2004.04004.x, 14979878View ArticlePubMedGoogle Scholar
- Roh JK, Kim JS, Ahn YO (1998) Epidemiologic and clinical characteristics of migraine and tension-type headache in Korea. Headache 38(5):356–365, 10.1046/j.1526-4610.1998.3805356.x, 9630788, 1:STN:280:DyaK1c3psVantg%3D%3DView ArticlePubMedGoogle Scholar
- Bigal ME, Liberman JN, Lipton RB (2006) Obesity and migraine: a population study. Neurology 66(4):545–550, 10.1212/01.wnl.0000197218.05284.82, 16354886View ArticlePubMedGoogle Scholar
- Stewart WF, Lipton RB, Liberman J (1996) Variation in migraine prevalence by race. Neurology 47(1):52–59, 8710124, 1:STN:280:DyaK283ptFSitw%3D%3DView ArticlePubMedGoogle Scholar
- Schwartz BS, Stewart WF, Simon D, Lipton RB (1998) Epidemiology of tension-type headache. JAMA 279(5):381–383, 10.1001/jama.279.5.381, 9459472, 1:STN:280:DyaK1c7hvFGlsg%3D%3DView ArticlePubMedGoogle Scholar
- Schwartz BS, Stewart WF, Lipton RB (1997) Lost workdays and decreased work effectiveness associated with headache in the workplace. J Occup Environ Med 39(4):320–327, 10.1097/00043764-199704000-00009, 9113602, 1:STN:280:DyaK2s3mvVemsw%3D%3DView ArticlePubMedGoogle Scholar
- Lipton RB, Scher AI, Kolodner K, Liberman J, Steiner TJ, Stewart WF (2002) Migraine in the United States: epidemiology and patterns of health care use. Neurology 58(6):885–894, 11914403, 1:STN:280:DC%2BD387ot1Wqtw%3D%3DView ArticlePubMedGoogle Scholar
- Kececi H, Dener S (2002) Epidemiological and clinical characteristics of migraine in Sivas, Turkey. Headache 42(4):275–280, 10.1046/j.1526-4610.2002.02080.x, 12010384View ArticlePubMedGoogle Scholar
- Celik Y, Ekuklu G, Tokuç B, Utku U (2005) Migraine prevalence and some related factors in Turkey. Headache 45(1):32–36, 10.1111/j.1526-4610.2005.05007.x, 15663610View ArticlePubMedGoogle Scholar
- Katsarava Z, Dzagnidze A, Kukava M, Mirvelashvili E, Djibuti M, Janelidze M, Jensen R, Stovner LJ, Steiner TJ (2009) Primary headache disorders in the Republic of Georgia: prevalence and risk factors. Neurology 73(21):1796–1803, 10.1212/WNL.0b013e3181c34abb, 19933983, 1:STN:280:DC%2BD1MjptFWntg%3D%3DView ArticlePubMedGoogle Scholar
- Zivadinov R, Willheim K, Jurjevic A, Sepic-Grahovac D, Bucuk M, Zorzon M (2001) Prevalence of migraine in Croatia: a population-based survey. Headache 41(8):805–812, 10.1046/j.1526-4610.2001.01147.x, 11576206, 1:STN:280:DC%2BD3MrjtVaqug%3D%3DView ArticlePubMedGoogle Scholar
- Zivadinov R, Willheim K, Sepic-Grahovac D, Jurjevic A, Bucuk M, Brnabic-Razmilic O et al (2003) Migraine and tension-type headache in Croatia: a population-based survey of precipitating factors. Cephalalgia 23:336–343, 10.1046/j.1468-2982.2003.00544.x, 12780762, 1:STN:280:DC%2BD3s3ls1emtw%3D%3DView ArticlePubMedGoogle Scholar
- Launer LJ, Terwindt GM, Ferrari MD (1999) The prevalence and characteristics of migraine in a population-based cohort: the GEM study. Neurology 53(3):537–542, 10449117, 1:STN:280:DyaK1Mzns1emtQ%3D%3DView ArticlePubMedGoogle Scholar
- Steiner TJ, Scher AI, Stewart WF, Kolodner K, Liberman J, Lipton RB (2003) The prevalence and disability burden of adult migraine in England and their relationships to age, gender and ethnicity. Cephalalgia 23(7):519–527, 10.1046/j.1468-2982.2003.00568.x, 12950377, 1:STN:280:DC%2BD3svns1GhsQ%3D%3DView ArticlePubMedGoogle Scholar
- Rasmussen BK, Jensen R, Schroll M, Olesen J (1991) Epidemiology of headache in a general population—a prevalence study. J Clin Epidemiol 44(11):1147–1157, 10.1016/0895-4356(91)90147-2, 1941010, 1:STN:280:DyaK38%2FksVKlsw%3D%3DView ArticlePubMedGoogle Scholar
- Russell MB, Kristiansen HA, Saltyte-Benth J, Kvaerner KJ (2008) A cross-sectional population-based survey of migraine and headache in 21,177 Norwegians: the Akershus sleep apnea project. J Headache Pain 9(6):339–347, 10.1007/s10194-008-0077-z, 18850259PubMed CentralView ArticlePubMedGoogle Scholar
- Hagen K, Zwart JA, Vatten L, Stovner LJ, Bovim G (2000) Prevalence of migraine and non-migrainous headache—head-HUNT, a large population-based study. Cephalalgia 20(10):900–906, 10.1046/j.1468-2982.2000.00145.x, 11304025, 1:STN:280:DC%2BD3MvntlShuw%3D%3DView ArticlePubMedGoogle Scholar
- Lilleng H, Bekkelund S (2009) Seasonal variation of migraine in an Arctic population. Headache 49(5):721–725, 10.1111/j.1526-4610.2008.01239.x, 19472449View ArticlePubMedGoogle Scholar
- Gourie-Devi M, Gururaj G, Satishchandra P, Subbakrishna DK (2004) Prevalence of neurological disorders in Bangalore, India: a community-based study with a comparison between urban and rural areas. Neuroepidemiology 23(6):261–268, 10.1159/000080090, 15297791, 1:STN:280:DC%2BD2cvnslChsw%3D%3DView ArticlePubMedGoogle Scholar
- Wong TW, Wong KS, Yu TS, Kay R (1995) Prevalence of migraine and other headaches in Hong Kong. Neuroepidemiology 14(2):82–91, 10.1159/000109782, 7891818, 1:STN:280:DyaK2M7pvVyntQ%3D%3DView ArticlePubMedGoogle Scholar
- Queiroz LP, Peres MF, Piovesan EJ, Kowacs F, Ciciarelli MC, Souza JA, Zukerman E (2009) A nationwide population-based study of tension-type headache in Brazil. Headache 49(1):71–78, 10.1111/j.1526-4610.2008.01227.x, 18793211View ArticlePubMedGoogle Scholar
- Queiroz LP, Peres MF, Kowacs F, Piovesan EJ, Ciciarelli MC, Souza JA, Zukerman E (2008) Chronic daily headache in Brazil: a nationwide population-based study. Cephalalgia 28(12):1264–1269, 10.1111/j.1468-2982.2008.01670.x, 18727642, 1:STN:280:DC%2BD1cjmslWntA%3D%3DView ArticlePubMedGoogle Scholar
- Maxwell JD (1994) Seasonal variation in vitamin D. Proc Nutr Soc 53:533–543, 10.1079/PNS19940063, 7886053, 1:CAS:528:DyaK2MXjslSmtL8%3DView ArticlePubMedGoogle Scholar
- Rapuri PB, Kinyamu HK, Gallagher JC, Haynatzka V (2002) Seasonal changes in calciotropic hormones, bone markers, and bone mineral density in elderly women. J Clin Endocrinol Metab 87(5):2024–2032, 10.1210/jc.87.5.2024, 11994336, 1:CAS:528:DC%2BD38XjsFGht7s%3DView ArticlePubMedGoogle Scholar
- Prince PB, Rapoport AM, Sheftell FD, Tepper SJ, Bigal ME (2004) The effect of weather on headache. Headache 44(6):596–602, 10.1111/j.1526-4610.2004.446008.x, 15186304View ArticlePubMedGoogle Scholar
- Soriani S, Fiumana E, Manfredini R, Boari B, Battistella PA, Canetta E et al (2006) Circadian and seasonal variation of migraine attacks in children. Headache 46(10):1571–1574, 10.1111/j.1526-4610.2006.00613.x, 17115990View ArticlePubMedGoogle Scholar
- Cugini P, Romit A, Di Palma L, Giacovazzo M (1990) Common migraine as a weekly and seasonal headache. Chronobiol Int 7:467–469, 10.3109/07420529009059158, 2097080, 1:STN:280:DyaK3M3ms1egsg%3D%3DView ArticlePubMedGoogle Scholar
- Marrelli A, Marini C, Prencipe M (1988) Seasonal and meteorological factors in primary headaches. Headache 28:111–113, 10.1111/j.1526-4610.1988.hed2802111.x, 3372236, 1:STN:280:DyaL1c3isleqsw%3D%3DView ArticlePubMedGoogle Scholar
- Garland CF, Garland FC (1980) Do sunlight and vitamin D reduce the likelihood of colon cancer? Int J Epidemiol 9(3):227–231, 10.1093/ije/9.3.227, 7440046, 1:STN:280:DyaL3M%2FmvVOktg%3D%3DView ArticlePubMedGoogle Scholar
- Grant WB (2006) Epidemiology of disease risks in relation to vitamin D insufficiency. Prog Biophys Mol Biol 92(1):65–79, 10.1016/j.pbiomolbio.2006.02.013, 16546242, 1:CAS:528:DC%2BD28XlsFKrsbk%3DView ArticlePubMedGoogle Scholar
- Hagen K, Vatten L, Stovner LJ, Zwart JA, Krokstad S, Bovim G (2002) Low socio-economic status is associated with increased risk of frequent headache: a prospective study of 22718 adults in Norway. Cephalalgia 22(8):672–679, 10.1046/j.1468-2982.2002.00413.x, 12383064, 1:STN:280:DC%2BD38njtlehug%3D%3DView ArticlePubMedGoogle Scholar
- Ginde AA, Liu MC, Camargo CA Jr (2009) Demographic differences and trends of vitamin D insufficiency in the US population, 1988–2004. Arch Intern Med 169(6):626–632, 10.1001/archinternmed.2008.604, 19307527, 1:CAS:528:DC%2BD1MXksVOnt74%3DPubMed CentralView ArticlePubMedGoogle Scholar
- Glendenning P, Taranto M, Noble JM, Musk AA, Hammond C, Goldswain PR, Fraser WD, Vasikaran SD (2006) Current assays overestimate 25-hydroxyvitamin D3 and underestimate 25-hydroxyvitamin D2 compared with HPLC: need for assay-specific decision limits and metabolite-specific assays. Ann Clin Biochem 43:23–30, 10.1258/000456306775141650, 16390606, 1:CAS:528:DC%2BD28XhtF2isrs%3DView ArticlePubMedGoogle Scholar
- Eyles DW, Smith S, Kinobe R, Hewison M, McGrath JJ (2005) Distribution of the vitamin D receptor and 1 alpha-hydroxylase in human brain. J Chem Neuroanat 29(1):21–30, 10.1016/j.jchemneu.2004.08.006, 15589699, 1:CAS:528:DC%2BD2cXhtVKktrrIView ArticlePubMedGoogle Scholar
- Jirikowski GF, Kauntzer UW, Dief Ael E, Caldwell JD (2009) Distribution of vitamin D binding protein expressing neurons in the rat hypothalamus. Histochem Cell Biol 131(3):365–370, 10.1007/s00418-008-0540-6, 19034485, 1:CAS:528:DC%2BD1MXpvVSrtg%3D%3DView ArticlePubMedGoogle Scholar