Oh, winter—where days are short, nights are long, and wind chill forces tears to your eyes. The decrease in temperature isn't ideal, but what I find most concerning is the lack of daylight. With notably less exposure to sunshine, I wondered whether I might soon find myself suffering from a Vitamin D deficiency. So I began to investigate.

First, a primer: Vitamin D helps the body to absorb phosphorous and calcium, which are essential to bone growth, Neica Goldburg, MD, cardiologist and director of the Joan H. Tisch Center for Women’s Health explains. And 66 percent of people worldwide have inadequate levels of it—leading to many problems, including insufficient bone density, fatigue, and muscle aches.

Now, you're no more likely to have a Vitamin D deficiency in the winter than you are at any other time. While exposure to ultraviolet light does create Vitamin D in your body, so do a lot of other things. Like food! Things like fish like tuna, swordfish, salmon, and sardines. Fortified foods like cows milk, juices, yogurts, and often ready-to-go cereals, provide Vitamin D as well, Leah Silberman, a clinical registered dietitian nutritionist, says. She recommends making an egg and shiitake mushroom omelet to double up on Vitamin D, too. Alternatively, you can take a daily multi-vitamin or Vitamin D supplement. Choose D3 (cholecalciferol) rather than D2 (ergocalciferol) if we're getting specific.

A common misconception (going back to the ultraviolet light) is that not wearing SPF while you're out and about is good idea because it ups your Vitamin D intake. Yes, it's true, sunscreen will block those UV rays and thus the production of Vitamin D, that’s no excuse to not wear it. Take it from dermatologist Peter Ehrnstrom, MD, of Alaska who says that even in the 49th state, “the number of skin cancers is overwhelmingly larger than the number of Vitamin D deficiencies.” It's also the number one cancer for young adults from 25 to 29.

A blood test from your healthcare provider is the only way to confirm your Vitamin D levels. Dr. Goldburg urges this option if you think you may suffer from a deficiency. She stresses if this is the case, food sources will not be sufficient alone and that the test will help your provider to determine the best course of action.

—Alexis Cheung

Photographed by Tom Newton.