Shedding light on vitamin D

Vitamin D is an essential nutrient that your body produces when your skin is exposed to sunlight, but there are ways to get it from foods too. It helps your body absorb calcium and maintains the calcium and phosphate your bones need to form and grow. It also contributes to cell growth, immunity, and nerve and muscle function, and it can help reduce inflammation. In addition, it plays key roles in reducing your risk of many adverse health conditions, including depression, cancer, heart disease, osteoporosis and others.

Sun exposure

Fair-skinned people can get enough from as little as 15 minutes in the sun; the darker your skin, the longer it will take (up to 2 hours), but less than it would take for your skin to burn. For many reasons, however, people often don’t get enough exposure. A little time outside on a sunny day with your arms and legs uncovered can provide nearly all the vitamin D most people need, but that can be challenging when you’re wearing a long-sleeved uniform, working inside all day, or in winter.

Vitamin D from foods

Unlike other nutrients, vitamin D occurs naturally in very few foods, so it can be difficult to get enough through your diet. That’s why some foods are “fortified” with vitamin D; that is, they have vitamin D added. The most common is milk, but some cereal products, yogurt, orange juice, margarine, and other foods also are fortified. Foods that naturally contain vitamin D include cod liver oil, swordfish, salmon, tuna, sardines, beef liver, and egg yolks.

How much vitamin D?

The Recommended Daily Allowance of vitamin D is 600 IU (except that infants under one year need only 400 IU and adults over 70 need 800 IU). On fortified food labels, look for “DV” (Daily Value) to make sure you get some in your diet if you don’t get enough sun on your skin. The 100% DV is only 400 IU, because it assumes you get some vitamin D from sun exposure and foods with natural vitamin D content. Foods fortified with vitamin D are required to list the amount and their label’s Nutrition Facts panel. However, natural vitamin D content isn’t required on food labels. If you want to find out the natural content in various foods, you can use the USDA Food Composition Databases.

Vitamin D supplements

Another way to get vitamin D is through supplements, especially for people who are deficient in this nutrient or have special medical needs. However, it’s important to consult a healthcare provider before taking supplemental vitamin D, because excess vitamin D can be stored in your body, putting you at risk for toxicity. Over time, too much vitamin D can lead to irregular heart rhythms, kidney damage, and other serious health problems. If you take large doses of supplemental vitamin D and eat foods that are fortified with it, you could easily obtain more than recommended amounts.

The bottom line

Despite the availability of vitamin D from all these sources, nearly one-fourth of people living in the U.S. have low vitamin D levels, which can lead to osteoporosis, autoimmune diseases, type 2 diabetes, certain types of cancer, and more. For more information about vitamin D, read this fact sheet from the Office of Dietary Supplements.

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