Winter is coming, watch your Vitamin D

By Kirstin Grace-Simons and By 2Lt. Sarah Nowroozian, Madigan dietetic internDecember 7, 2022

(Photo Credit: U.S. Army) VIEW ORIGINAL

MADIGAN ARMY MEDICAL CENTER, Joint Base Lewis-McChord, Wash. – Winter is on the horizon here in the Pacific Northwest. The rainy season has begun, temperatures are dropping and daylight hours are getting shorter and shorter. With darker days ahead and more time spent indoors, a real health threat lurks in the shadows – vitamin D deficiency.

According to the National Health and Nutrition Examination Survey (NHANES), roughly half of the U.S. population is vitamin D deficient.

“Service members are not excluded from the high prevalence of vitamin D insufficiency, particularly those assigned to duty stations above the 35th parallel, such as Joint Base Lewis-McChord, Wash. Striving for a sufficient level of vitamin D can help prevent respiratory illness, reduce the risk of musculoskeletal injuries and optimize performance and readiness,” said Dr. Mary McCarthy, a senior nurse scientist at Madigan Army Medical Center who has conducted extensive research on vitamin D.

Vitamin D is an essential micronutrient aiding in many processes throughout the body. This hormone plays an important role in bone health by regulating calcium and phosphorus. A deficiency can result in the softening and weakening of bones. Over time, rickets in children and osteoporosis in adults may occur. Deficiencies have also been linked to declines in mental health, resulting in seasonal affective disorder and depression.

Vitamin D is often referred to as the “sunshine vitamin” because of the skin’s natural ability to produce vitamin D when exposed to sunlight. Ideally, spending 10-15 minutes outside during the spring and summer months should maintain adequate vitamin D levels all year round.

Most people don’t get enough vitamin D from sunlight alone, however. Reasons vary and include: skin type, sunscreen use and overcast weather. With the winter months settling in, getting enough vitamin D becomes especially challenging.

What are other ways for individuals to get vitamin D?

Very few foods naturally contain vitamin D. These include animal-based foods and mushrooms, with fatty fish and fish liver oils among the best sources. The recommended dietary allowance (RDA) for adults and children one year of age and older is 15 mcg (600 international units [IU]). This jumps up to 20 mcg (800 IU) for those over 70.

“While it can be a challenge to find food sources of vitamin D that appeal to you, many foods are fortified, such as cow’s milk, orange juice, cereals and oatmeal. Also, newer choices on the market include plant-based milk options and eggs, especially from chickens raised outside in the sunlight or with vitamin D-enriched feed – who knew?! You will need to check the labels to find out the vitamin D content as it can vary widely,” said McCarthy.

Nevertheless, food is still not enough…

An analysis from the NHANES found that daily vitamin D intake was low. On average, men consumed 5.1 mcg (204 IU) while women consumed 4.2 mcg (168 IU). Children aged 2-19 years consumed a little less than men at 4.9 mcg (196 IU).

How can individuals get enough vitamin D?

“Choose your vitamin D dietary supplement carefully. Third party certification ensures that products have successfully passed the quality, safety, performance and claims-of-benefit analysis; look for the U.S. Pharmacopeial Convention or USP verified mark on the product package," said McCarthy.

Supplementing vitamin D can help bridge the gap and prevent a deficiency. Many multivitamins and multimineral supplements contain vitamin D. Standalone vitamin D supplements are also available. Look for vitamin D3 over D2, as D3 is more effective. Vitamin D is fat-soluble, so it is best absorbed when taken with food containing fat.

Be aware that too much vitamin D can be harmful. The Food and Nutrition Board recommends adults consume no more than 100 mcg (4,000 IU) per day. The body limits the amount of vitamin D it makes from the sun. However, consuming too much can cause nausea, vomiting and kidney failure.

Overall, vitamin D will be crucial over the upcoming months. Try to add foods rich in vitamin D to your meals as well as add a supplement containing vitamin D to your daily regime. These simple steps can help safeguard against a deficiency.

To learn more, visit the Office of Dietary Supplements website ( or make an appointment with the Nutrition Care Division at Madigan Army Medical Center.

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