In 2006 the CDC reported that one quarter of the population was deficient in vitamin D. UVB rays from the sun help our bodies produce vitamin D, so it may be that our modern lifestyle spent mostly indoors affects our vitamin D production. Additionally, sunscreen blocks UVB rays from reaching our skin, which could also reduce vitamin D production.
As the days grow shorter in winter, people are exposed to even less sunlight. Several studies supported that increased exposure to sunlight noticeably improved the mood of those with Seasonal Affective Disorder. A number of other reviewed studies found a strong relationship between low vitamin D levels and depression.
Although there’s some support for this linkage, there’s still the issue of causality. Does depression lower vitamin D levels? Or do lower vitamin D levels contribute to depression? This is an area that needs more research.
A few things to keep in mind are that the sun’s rays needed to produce vitamin D cannot pass through glass, so you actually need to go outside to receive the benefits. Also, you need to have high enough vitamin D levels to absorb calcium, so this vitamin does not only relate to depression but overall body function. Finally, it does take time to bring up vitamin D levels, so if you need to increase your vitamin D, plan on months not days.
If you want to test your vitamin D levels, a simple blood test will do. If results show a deficiency, you may want to add a vitamin D supplement or find ways to get outside more during the day (which can be tough in North Dakota when the temperature fall below zero!). Be sure to talk to your doctor before adding any new supplements to your diet.