A newly discovered link between low levels of vitamin D and depression may shed light on why winter’s wan sun leaves some feeling glum. A Dutch study of over 1,200 seniors found 14% lower levels of vitamin D among those reporting more feelings of loneliness and listlessness. Other recent research found chronic pain problems more prevalent among those lacking vitamin D. In particular, D deficiency doubled women’s risk of serious lower back pain, in one University of Delaware study.

Since sunshine naturally prompts the body to produce vitamin D, shorter days may lower levels. Deficiency is on the rise among kids — and is more prevalent among seniors, darker skinned ethnicities and the obese (who produce 57% less vitamin D than their normal-weight peers). You can get vitamin D from canned salmon and sardines. Milk, juice and cereal are often fortified with vitamin D.

This new evidence of this nutrient’s importance to minimizing pain and maximizing happiness lengthens a long list of vitamin D benefits, including healthy bones and teeth, lower blood pressure, improved immunity and reduced risk of certain cancers. A University of California San Diego study found a 50% drop in colon cancer and a 30% decreased risk of ovarian and breast cancer with increased intakes of vitamin D — which also reduced prostate cancer risk by 43%.

Published January 1, 2009