Study finds no link between vitamin D deficiency and SAD
Winter is synonymous with skiing, tobogganing and hot cocoa. But for many, it is the season of the blues. With winter come shorter days and less sunlight, and a lack of vitamin D has been linked to depression and the symptoms of seasonal affective disorder (SAD). But researchers from the University of Warwick in the UK have found that there is no clear link between vitamin D levels in the blood and depression. Their findings are published in the Journal of Affective Disorders. SAD typically affects people who have normal mental health throughout most of the year. Sufferers experience serious mood changes when the seasons change, including depression and excessive sleep, as well as lethargy and hunger pangs. In the past, researchers have said that exposure to sunlight stimulates vitamin D in the skin and reduced sunlight in winter could be responsible for SAD. But the UK research team has discovered that low levels of vitamin D in the blood may not be connected to depression. Led by Professor Oscar Franco from Warwick Medical School, the researchers conducted a population-based cross-sectional study and tested the levels of vitamin D (25-hydroxyvitamin D or 25(OH)D) in 3 262 subjects from Beijing and Shanghai, China, as part of the 'Nutrition and Health of Aging Population in China' (NHAPC) project. A questionnaire was then given to them to assess the prevalence of depressive symptoms. Symptoms of depression were defined as a score of 16 or higher on the Center for Epidemiological Studies of Depression Scale (CES-D). The team, cooperating with colleagues from the Institute for Nutritional Sciences, Chinese Academy of Sciences in China, used radioimmunoassay (a method for measuring minute amounts of a substance in the blood) to measure circulating vitamin D concentrations. In the study, the researchers found that there was a lower prevalence (7.2%) of depressive symptoms in the top tertile of 25(OH)D concentrations compared to the lowest tertile (11.1%). 'This association was substantially attenuated after controlling for various confounding factors, and disappeared after including geographic location in the model,' the researchers wrote. Experts say vitamin D deficiency is triggered when the concentration of 25-hydroxyvitamin D in the blood serum is at 12 nanograms/millilitre (ng/ml) or less. The normal concentration of 25-hydroxyvitamin D in the blood serum is 25-50 ng/ml. 'Few studies have explored the association between blood 25-hydroxyvitamin D concentrations and depression in the general population,' explained Professor Franco. 'A deficiency of vitamin D has also been attributed to several chronic diseases, including osteoporosis, common cancers, autoimmune and cardiovascular diseases,' he added. 'Previous studies into the effects of vitamin D supplementation have produced mixed results. More studies are still needed to evaluate whether vitamin D is associated with seasonal affective disorders, but our study does raise questions about the effects of taking more vitamin D to combat depressive symptoms.' Data from past research indicate that 1.3-3% of Europeans suffer from SAD, against 0.8-9.7% of North Americans and 0-0.9% of Asians. Researchers have also found that 70-80% of SAD sufferers are women, with the most common age of onset in the 30s.
Countries
China, United Kingdom