Let There be Light: The Importance of Sunshine
The northern latitude of Seattle allows its residents to make vitamin D from sunshine for only eight months out of the year, but excess amounts are stored for use in the winter, so be sure to soak it up while you can.
One of the most talked-about nutrients, vitamin D, doesn’t act like a vitamin at all — it works like a hormone. The term “vitamin” implies something essential that must come from our food, but we can make enough vitamin D if we get adequate sun exposure.
Vitamin D affects multiple systems in the body, especially bones and the immune system, and works by changing how genes are expressed — just like a hormone does. It is made by the skin when it’s exposed to sunlight, specifically to UVB rays, then converted into its active form by the liver and kidneys.
Seattle lies around 47 degrees north of the equator, which means that we can only make vitamin D from sunshine from mid-March to mid-October. During these months, 15 minutes of noontime sun exposure on the hands, arms and face will provide a person with the equivalent of 1,000 IU of vitamin D. That amount is lower for people with darker complexions, who may need to double their time in the sun. Excess vitamin D made from sun exposure is stored and can be used during the long, gray winter months.
Vitamin D’s main function is to regulate the amount of calcium and phosphorus in the blood, which is essential to keep nerves firing and the heart beating. When calcium levels drop, vitamin D production increases so that more calcium is absorbed from food. If there’s not enough calcium from food, vitamin D sends signals to use calcium from bone, eventually making bones weaker.
Deep in the bone marrow, vitamin D signals developing immune cells to mature. These signals strengthen the immune response and stop cells from attacking the body’s own cells (autoimmunity). Many studies have shown that low levels of vitamin D in the blood are associated with the development of autoimmune diseases. These include diseases like type 1 diabetes, multiple sclerosis, rheumatoid arthritis and lupus. When coupled with other risk factors, a deficiency of vitamin D creates immune cells that don’t know the difference between a bacterium and a brain cell.
According to the Linus Pauling Institute, vitamin D has also been shown to play a role in lowering the risk of breast, colon and prostate cancers, helpful in controlling high blood pressure, slowing cognitive decline in Alzheimer’s disease, and treating Crohn’s disease and eczema, among other conditions.
If vitamin D is so important, then shouldn't everyone be taking the “sunshine vitamin,” just to be sure that they're getting enough? According to the latest recommendations from the U.S. Preventative Services Task Force, that’s not the case. Only people who are at risk for deficiency, such as people who have a chronic illness or older adults at risk for falls, should have their vitamin D levels routinely checked and receive supplementation. As for the rest of us — go outside, it’s good for you.
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