Vitamin D is a health superstar, supporting your body from head to toe. Research suggests that it plays a key role in building strong bones and muscles, keeping your immune system and your cardiovascular system strong, and helping you maintain a sunny outlook. And yet, 35% of adults in the United States are deficient in vitamin D, according to the Cleveland Clinic, primarily because it’s difficult to get sufficient amounts from your diet.

Meet the expert: Michael F. Holick, Ph.D., M.D., a professor of medicine at Boston University School of Medicine and author of The Vitamin D Solution.

Here, doctors share surefire ways to get more vitamin D and guarantee you have enough to achieve optimal health.

Bask in the sun.

“Sunlight is your best source for D,” said Michael F. Holick, Ph.D., M.D., a professor of medicine at Boston University School of Medicine and author of The Vitamin D Solution. When sunlight hits your bare, un-SPF’d hide, your skin cells synthesize those rays into vitamin D. Of course, sun exposure also comes with cancer risks. Fortunately, even brief exposure without protection can net you the D you need. Dr. Holick developed the app dminder; by plugging in your location, time zone, and skin type, the app will tell you how much vitamin D you’re making (it will vary based on the time of day, season, and your location) and when to get out of the sun.

Supplement with D3.

The National Institutes of Health (NIH) recommend adults get 600 to 800 IU of vitamin D every day. But Dr. Holick recommended much more—1,500 to 2,000 IU a day. At that level, there’s no risk of overdoing it, and he said your body needs that amount for you to reap all of the vitamin’s benefits. (Dr. Holick shared that he takes 4,000 IU a day year-round, even though he’s outside during the summer cycling, gardening, and playing tennis.) Vitamin D toxicity is possible, according to the National Library of Medicine, but you would need to take more than 10,000 IU every day to reach dangerous levels.

While you can get some D in a multivitamin, taking a D supplement on its own is the best way to get the amount Dr. Holick suggested. Look for a supplement that contains vitamin D3, the form that is naturally produced in the body and found in animal foods, recommends the Harvard T.H. Chan School of Public Health. Research has shown that D3 supplements tend to raise blood concentrations more and sustain those levels longer than vitamin D2, which is the form found in plants.

Enjoy wild salmon.

It’s not easy to get adequate vitamin D from diet alone. But you can find a decent amount in salmon. A 3-ounce portion of salmon will deliver between 383 and 570 IUs of vitamin D, depending on the type, according to the Dietary Guidelines for Americans. An even better source is cod liver oil—assuming your taste buds can handle it. Nordic Naturals Arctic-D Cod Liver Oil delivers 1,000 IU of vitamin D3 per teaspoon.

Add more mushrooms.

The mushroom industry figured out something genius: ‘Shrooms exposed to UV light produce vitamin D2 much like your skin cells do, thanks to the presence of ergosterol, a compound that acts as a precursor to vitamin D, per the Harvard T.H. Chan School of Public Health. So when you’re out shopping, look for mushrooms that say “vitamin D” on the label, which can contain as many as 1,000 IU per serving. This last step is key, as the amount of vitamin D found in mushrooms will vary based on where they were grown and how much light they have been exposed to.

Eat fortified foods.

Food manufacturers pump up some products by adding vitamin D during processing. In general, a cup of D-fortified orange juice or milk contains around 100 IU, per the Dietary Guidelines for Americans. Many breakfast cereals also offer some D—usually 40 to 100 IU per serving. Just be sure to check the label before you leave the store, as not all of these products contain an added dose of vitamin D.

Dietary supplements are products intended to supplement the diet. They are not medicines and are not intended to treat, diagnose, mitigate, prevent, or cure diseases. Be cautious about taking dietary supplements if you are pregnant or nursing. Also, be careful about giving supplements to a child, unless recommended by their healthcare provider.

This story was originally published in 2015 and has since been updated.

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