Primary headaches, including migraine, are among the leading health problems and causes of disability in the modern working population1. Currently, there is a global trend in chronification of migraine and a growing number of cases of medication overuse headache due to improper use and/or overuse of painkillers2,3. Interestingly, medication overuse headache could develop not only due to overuse of opioids but even after ‘specific’ anti-migraine treatments with triptans4. Intractable forms of migraine resistant to specific anti-migraine treatments and ‘epidemics of medication overuse headache’ are raising an issue of more complex approaches on headache cure, including nutritional approach.

The role of vitamin D is widely discussed recently as the key dietary factor determining the likelihood of various neurovascular diseases5,6. This issue is of key importance to Nordic countries, including Finland, Sweden, Norway, Denmark, and other areas with limited year-round UVB exposure from the sun. Headache prevalence has been suggested to be related to increasing latitude and possibly to be less prevalent during summer7, suggesting a possible role for vitamin D exposure. However, there is little data regarding the association between vitamin D exposure and headache. In a small case-control study, vitamin D receptor polymorphisms were found to be more prevalent in migraine patients than in controls and be related to severity of headache8. In a cross-sectional study from Norway, non-smoking participants with migraine or non-migraine headache had lower serum 25(OH)D concentration9, whereas no difference was observed among smokers. Low serum 25(OH)D concentration was also associated with slightly higher odds for non-migraine headache, but not for migraine9. In contrast, in another case-control study, serum 25(OH)D concentration did not differ between controls and migraine patients10. In another study from Norway, headache was more prevalent among those with serum 25(OH)D <50 nmol/L11.

In three case-reports, supplementation with vitamin D and calcium reduced migraine attacks12,13,14. However, results from larger, randomized, placebo-controlled vitamin D supplementation trials have been mixed15,16. Recently, combined therapy with simvastatin and vitamin D 3 reduced the number of days with migraine17. This finding supported the previous cross-sectional observation from the same study group that statin use was associated with lower odds for severe headache or migraine only among those with higher serum 25(OH)D concentrations18.

Overall, the study findings are inconsistent and many studies are small in size. Therefore, the purpose of our study was to investigate the associations between serum 25(OH)D and risk of frequent headache among 2601 middle–aged and older men from a population-based cohort study from eastern Finland.