Vitamin D 101: Why Food, Sun, and Supplements All Matter
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Allison Edwards, MS, RDN, LDN, CLC
Vitamin D plays an essential role in overall health, supporting bone strength, immune function, muscle health, and even mood regulation (Holick, 2007). The Recommended Dietary Allowance (RDA) for vitamin D is 400 IU (10 mcg) per day for infants, 600 IU (15 mcg) per day for children and adults ages 1–70, and 800 IU (20 mcg) per day for adults over age 70, according to the National Institutes of Health. You can obtain vitamin D from three main sources: food, sunlight, and supplements. It is often referred to as the “sunshine vitamin” because your body can produce it when your skin is exposed to ultraviolet B (UVB) rays from the sun. While this sounds simple, there are several reasons why relying on sunlight alone is often not enough.
For people with lighter skin, approximately 5-10 minutes of midday sun exposure on the face and arms may produce enough vitamin D for the day. Individuals with darker skin require more time in the sun to generate the same amount because higher levels of melanin reduce vitamin D synthesis (Wacker & Holick, 2013). Geography also plays a major role. If you live north of the 34th latitude (roughly Atlanta, Georgia) the sun’s rays are too weak from October through April to allow your body to make vitamin D, even on sunny days (NIH Office of Dietary Supplements [ODS], 2024). On top of that, vitamin D is fat-soluble and can be stored in the body, but those stores typically only last one to two months. This means that even if you get ample sun exposure during the summer, it may not carry you through the fall and winter months (Holick, 2007).
Sun protection further complicates the picture. Sunscreen can block 95–99% of vitamin D production in the skin, but skipping sunscreen is not recommended due to the increased risk of skin cancer and premature skin aging (Harvard T.H. Chan School of Public Health, 2024). Unless you live close to the equator and spend significant time outdoors without sun protection (which is not advised), most people cannot rely on sunlight alone to meet their vitamin D needs.
Dietary sources of vitamin D can help, but they are limited. Foods that contain vitamin D include fortified cow’s milk; fatty fish such as salmon, trout, tilapia, flounder, and sardines; egg yolks; mushrooms grown in natural sunlight; fortified cereals; yogurt; kefir; and fortified orange juice. While these foods contribute to vitamin D intake, it can be difficult to meet daily needs through food alone. For example, a child would have to consume 9-10 eggs, 3 oz salmon, or up to 12 pounds of mushrooms DAILY to reach the MINUMUM recommended amount of vitamin D.
Because of these challenges, many people fall short of optimal vitamin D levels. This is why it’s important to talk with your healthcare provider about whether you should have your vitamin D level checked. Based on your results, lifestyle, and individual health needs, a provider may recommend a vitamin D3 supplement to help you meet your needs safely and effectively (CDC, 2024). As a registered dietitian, I encourage viewing vitamin D as a nutrient that often requires a combination approach to support long-term health: smart sun exposure, food sources when possible, and supplementation when needed.
Works Cited
Holick, M. F. (2007). Vitamin D deficiency. The New England Journal of Medicine, 357(3),
266–281. https://doi.org/10.1056/NEJMra070553
National Institutes of Health, Office of Dietary Supplements. (2024). Vitamin D—Fact sheet
for health professionals. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
Centers for Disease Control and Prevention. (2024). Vitamin D.
Harvard T.H. Chan School of Public Health. (2024). Vitamin D.
Wacker, M., & Holick, M. F. (2013). Sunlight and vitamin D: A global perspective for health.
Dermato-Endocrinology, 5(1), 51–108. https://doi.org/10.4161/derm.24494
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