Looks like scientists have figured out what vitamin “D” might stand for: A new study links depression to low levels of vitamin DAssociation between low serum 25-hydroxyvitamin D and depression in a large sample of healthy adults: the Cooper Center longitudinal study. Hoang, M.T., Defina, L.F., Willis, B.L, et al. Department of Psychiatry, UT Southwestern Medical Center at Dallas, TX, USA. Mayo Clinic Proceedings 2011;86(11):1050-5.. And Americans should definitelytake note, since most of us are falling behind the curve— one in 10 adults in the USA are deficient in vitamin DDemographic differences and trends of vitamin D insufficiency in the US population, 1988-2004. Ginde, A.A., Liu, M.C., Camargo, C.A. Department of Emergency Medicine, University of Colorado Denver School of Medicine, Aurora, CO. Archives of Internal Medicine, 2009 Mar 23;169(6):626-32..

Scientists have known for a while that Calcitriol, an active vitamin D hormone, affects neurotransmitters connected to mental disorders, but this is the largest study that directly links vitamin D and depressionVitamin D, light and mental health. Humble, M.B. Department of Clinical Neuroscience, Division of Psychiatry, Stockholm, Sweden. The Journal of Photochemistry and Photobiology B, 2010 Nov 3;101(2):142-9. Epub 2010 Aug 10.. Researchers followed 12,600 participants for four years and found people with low vitamin D levels were more likely to experience depressive symptoms (can’t only blame that stupid ex). The correlation was especially strong in people who had been depressed before. But let’s see the glass half full— higher vitamin D levels were associated with a decreased risk of depression for people with a history of the disorder.

Still, some mystery remains. Researchers aren’t sure whether low levels of vitamin D cause depressive symptoms, or whether depression decreases vitamin D levels. The study also didn’t say whether increasing vitamin D levels can reduce symptoms of depression in people with the disorder.

Other research suggests vitamin D insufficiency can contribute to osteoporosis, high blood pressure, and heart disease— meaning it’s worth amping up the amount of D in a diet. The Food and Drug Administration recommends we get between 200 and 800 IU vitamin D daily (a can of tuna contains 200 IU). So stock up on salmon, tuna, milk, and Swiss cheese— all super sources of vitamin D. Our bodies also produce vitamin D through exposure to the sunVitamin D, sun, sunbeds and health. Moan, J, Baturaite, Z, Juzeniene, A, et al. Department of Radiation Biology, Institute for Cancer Research, Oslo, Norway. Public Health Nutrition, 2011 Oct 24:1-5.. But a flight to the Bahamas isn’t necessary: 15 minutes of soaking up the sun a few days a week is all it takes. (The Caribbean does sound nice though…) Even in winter, though, protect the skin and keep the sunscreen on!