Can I get enough vitamin D through exposure to sunlight?

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Jonathan B. Levine, DMD
Prosthodontics
Our body’s ability to absorb vitamin D through synthesis of sunlight is geographically and seasonally dependent. For those people who live north of 40 degrees latitude (i.e., San Francisco, Denver and Philadelphia), they are unable to produce vitamin D during the winter months because the sun is at too low of an angle in the sky. Even when winter is nearing its end, aim to incorporate foods rich in vitamin D to help reverse any deficiencies. It’s naturally present in salmon, tuna, cheese and egg yolks and is fortified in the majority of the US milk supply, margarine, ready-to-eat breakfast cereals, orange juice and yogurt.

This content orignally appeared on doctoroz.com.
There is no safe amount of unprotected sun exposure, due to risk of skin cancer. Medical organizations including the American Academy of Pediatrics and the American Academy of Dermatology recommend that you obtain vitamin D from a healthy diet that includes food naturally rich in vitamin D, foods fortified with vitamin D, milk and other beverages fortified with Vitamin D and dietary supplements. I recommend that all of my patients protect themselves from the sun and take a daily vitamin with a vitamin D.
Keri Peterson, MD
Internal Medicine
Getting your vitamin D from sun exposure can be risky because it may also increase your risk of skin cancer, says internal medicine specialist Dr. Keri Peterson. To learn how to get adequate vitamin D without exposing your skin to harmful rays, watch this video.
David Slovik, MD
Endocrinology Diabetes & Metabolism
Vitamin D is made in the skin after exposure to sunlight. Some people make all the vitamin D they need by going outside for a few minutes a day without sunscreen. You should keep your exposure time short -- just 10 to 15 minutes a day -- to protect against skin cancer.
 
However, it's likely that sunlight alone won't generate adequate amounts of vitamin D. For example, if you live above 40 degrees latitude (the latitude of Denver, Indianapolis, and Philadelphia), the winter sunlight isn't strong enough to enable you to produce significant amounts of vitamin D. Sunscreen, glass, and clothing also interfere with this process, diminishing your ability to produce the vitamin. And as you age, your skin can't produce vitamin D as readily, and your intestines have more difficulty absorbing this vitamin.
Dr. Robin Miller, MD
Internal Medicine
Lots of people think the best way to get vitamin D is from the sun, but it's actually not, says Dr. Robin Miller. To find out the safest and most reliable way to get your vitamin D, watch this video.
Your skin is a vitamin D factory that runs on sunlight, but how much it produces depends on many factors. These include where you live (e.g., Miami has more sunny days than Seattle, and the sun is more intense there too), time of year (winter sun isn’t as strong as summer sun), how much time you spend outside (it doesn’t matter where you live if you stay indoors all day), what you wear when you’re outside (consider long sleeves, long pants and a hat vs. a bikini), whether you use sunscreen or not (it’s much better for your skin if you do, but not for your vitamin D production), skin type (the darker your skin, the more sun it needs to make vitamin D), and age (a person over 65 makes one-fourth as much as a 20-something). Overall, your skin can make all the vitamin D you need, but chances are good that it doesn't. According to some estimates, more than a billion people worldwide do not get enough vitamin D.
Sunlight is an excellent source of the vitamin D our bodies need to keep our bones healthy. Because it is fat-soluble, the body can store it, meaning casual exposure to sunlight in the summer months can provide ample amounts of this vitamin during the winter months. A 15- to 20-minute walk several times a week should keep your body well stocked. However, some studies find that those who work in offices year-round, whose sun exposure is limited through windows, and older adults need extra help. Aging reduces the capacity of the skin to use sunlight to produce vitamin D, so adults over age 65 need twice the amount of calcium daily -- 800 IU -- as most children and young adults. Certain sunscreens also can limit your body’s absorption of this vitamin. To get adequate amounts, use a standard multivitamin and add fortified milk, fortified cereal, salmon, tuna, herring, and mackerel to your diet.
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You can get vitamin D from two sources: the sun, and from things you put in your mouth (meaning food and supplements).

The sun actually triggers a chemical reaction that turns inactive vitamin D into active vitamin D, but most people aren't exposed to enough sun to get the recommended amount of D (and prolonged exposure can increase your risk of skin cancer; sun block also blocks out the vitamin D conversion).

The sun does not have enough energy north of a line between Los Angeles and Atlanta to convert inactive to active vitamin D between October 1st and April 15th, so many of us cannot get active vitamin D from sunlight even if we sit outside and bask in it all day.

So getting your vitamin D through food and supplements make the most sense.

Some foods, like fish and shellfish, have vitamin D naturally, while other foods like milk, 100-percent natural orange juice, and cereal often are or can be purchased fortified with it. Since most adults don't eat enough milk or orange juice or cereal, supplementing your diet with D can give you the levels you need. Make sure you choose a supplement that has the right dosage of vitamin D for you.
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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.