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Nutrition

What's the Deal With Vitamin D?

Why You Need It and How to Get It

What does your body make with help from the sun that plays a key role in bone health? The answer is Vitamin D, and your skin produces it by using sunlight. Your body needs vitamin D to absorb calcium, a building block for your bones. Vitamin D and calcium work together to regenerate bone cells, keeping your bones strong and healthy.

Vitamin D plays other roles in keeping your body healthy and functioning well. It may help:

  • Your immune system fight invaders like bacteria and viruses
  • Muscle strength
  • Reduce inflammation
  • Boost your mood
  • Protect against some types of cancers
  • Protect against Type 2 diabetes by improving your blood glucose (blood sugar) metabolism

Many people do not get enough vitamin D. Low levels can contribute to weak bones or osteoporosis. If you have low vitamin D levels, your symptoms might include fatigue or muscle pain, weakness or cramps. Or, you may have no signs or symptoms at all.

It is rare but possible to get too much vitamin D, which can be very harmful to your body. It is hard to get too much vitamin D from food alone, but you might get too much vitamin D if you take too much in the form of a supplement. The only way to determine your vitamin D level is through a blood test ordered by your primary care provider.

Your Daily Dose

Vitamin D is measured in “international units” (IUs), and the amount you need each day depends on your age and other health factors. In general, people ages one to 70, including women who are pregnant or breastfeeding, should get 600 IUs of vitamin D daily. People older than 70 may need more vitamin D to help maintain bone health. It is important to talk with your primary care provider about how much vitamin D you need before starting supplementation on your own.

How to Get It

Your skin makes vitamin D when it’s exposed to the sun. Most people receive the vitamin D they need through sun exposure.

“However, it’s important to remember that the amount of vitamin D your skin makes will also vary with your skin type, latitude, season and time of the day,” says Northwestern Medicine Integrative Medicine Physician Anna B. Shannahan, MD.

Very few foods naturally contain Vitamin D. In fact, vitamin D is found mostly in fortified foods, which are foods with nutrients added to them. In the U.S., ready-to-eat breakfast cereals and milk (including plant-based milk alternatives), and some brands of yogurt, orange juice and other food products are fortified with vitamin D. Vitamin D is found naturally in:

  • Fatty fish like tuna and salmon
  • Beef liver
  • Cheese
  • Egg yolks
  • Mushrooms treated with ultraviolet light

Vitamin D Do's

  • Talk with your physician about personalizing your vitamin D supplementation, especially if you live somewhere with limited annual sun exposure. Vitamin D can also interact with certain medications, so taking it under the guidance of a physician is important.
  • If you need to take vitamin D as a supplement, take it in the form of D3, which is the most effective form, according to Dr. Shannahan.

Vitamin D Don’ts

  • Don’t be unsafe with sun exposure to get your vitamin D. “You can still get vitamin D through sunscreen,” says Dr. Shannahan. If you’re spending time in the sun, wear sun protection to minimize your risk of skin cancer and skin damage.
  • Don’t take very high doses, or megadoses, of vitamin D.
Anna B. Shannahan, MD
Anna B. Shannahan, MD
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Assistant Professor, Feinberg School of Medicine
  • Primary Specialty Family Medicine
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