Vitamin D: The Sunshine Vitamin!

Jonathan Wanagat, MD, PhD

This article is the second in a series by Advisory Council Member Dr. Jonathan Wanagat. Dr. Wanagat will be offering monthly information and updates on healthcare issues of interest to seniors and caregivers.

Winter weather has just started in Puget Sound, and already, we treasure every break in the clouds and hope for a few sunny days.  In this month’s "Healthy Aging Tips," we are taking a closer look at a vitamin that also enjoys a moment in the sun and its important health benefits.

What is vitamin D?

Vitamin D, like all vitamins, is a natural compound that is required in small amounts for healthy living.  This important vitamin is produced in our skin with exposure to sunlight and is found naturally in some foods and is fortified in others.  Many of us also take vitamin D as part of a multivitamin or other supplement.

Whether from our skin, diet or supplements, our liver and kidneys convert vitamin D into more useful forms.  These variations of vitamin D help us control the levels of calcium and phosphorus in our blood, build strong bones and help our immune system fight infections.

Where do we get vitamin D?

The biggest source of vitamin D is our own skin. Exposure of skin to ultraviolet rays in sunlight converts a type of cholesterol into vitamin D. Spending five to ten minutes in the sun can produce about 3,000 International Units (IU) of vitamin D! The amount of vitamin D produced in the skin depends on the amount of sun exposure, which is affected by many variables such as sunscreen use, skin pigment, age, season, distance from the equator, and time of day. Sunscreen, which is important for the prevention of skin cancer, decreases the amount of vitamin D, and as you might guess, living in the American Northwest means less sun exposure and lower levels of vitamin D. In fact, above a latitude of 35 degrees north (approximately Los Angeles, California) very little if any vitamin D can be produced from November to February because of the short days and low angle of the sun in the sky!

The remainder of vitamin D is absorbed from our food and nutritional supplements. Fortunately for us in the Puget Sound area, many foods high in vitamin D are readily available, especially fatty fish such as salmon. One serving of fresh, wild salmon has about 800 IU of vitamin D. Foods fortified with vitamin D typically contain about 100 IU per serving, as is found in a glass of fortified milk, fortified orange juice or fortified breakfast cereals.

Nutritional supplements are another common and convenient source of vitamin D and are important for those of us with minimal sunlight exposure or other reasons for low vitamin D levels. A typical multivitamin contains 400 IU, while vitamin D supplements can range from 400 to 2,000 IU.

How much vitamin D is enough?

The current recommended daily value for the vitamin depends on your age. For adults up to age 50, the government recommends 200 IU each day.  For ages 51 to 70 the recommended amount is 400 IU each day and for those older than age 71, the recommendation is for 600 IU each day.

Recent studies suggest that many Americans require higher supplementation and many professionals, myself included, recommend 800 IU each day for individuals over 65.

Why is my vitamin D low?

There are many reasons to have a low vitamin D level. Factors that interfere with the skin’s ability to make vitamin D include lack of sun exposure, sunscreen, darker skin pigmentation and aging. Gastrointestinal problems and some medications can interfere with the absorption of vitamin D from the diet. Liver and kidney problems can prevent the vitamin D from being converted to more active forms.  Fortunately, in all of these cases, supplemental vitamin D can increase the levels to normal.

What’s so good about having enough vitamin D?

In addition to the importance of vitamin D for strong bones and a healthy immune system, exciting recent studies have shown that having sufficient amounts of vitamin D can help prevent osteoporosis and hip fractures. Similar studies have shown increases in muscle strength and decreases in the risk of falls with vitamin D supplementation. A few other studies have suggested intriguing associations between adequate vitamin D levels and decreased risk of heart disease and cancer.

Can I have too much vitamin D?

Too much of a good thing can often cause trouble, but vitamin D intoxication is extremely rare and usually caused by someone accidentally taking too much supplementation. Current recommendations are for no more than 2,000 IU each day. Interestingly, the skin is able to regulate its own production of vitamin D and does not make more than you need, and it would be difficult to have too much through one’s diet.

How can I make sure I’m getting enough vitamin D?

An important first step is to talk with your medical provider, who can review your dietary vitamin D intake and may suggest a laboratory test to check your vitamin D levels.  Based on the diet review and lab tests, you and your physician can decide whether you might benefit from additional vitamin D and the best method of supplementation.

Sources

1) Office of Dietary Supplements. National Institutes of Health. Dietary supplement fact sheet: Vitamin D, 2004 (updated 2007). 

2) U.S. Department of Agriculture (USDA) and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2005.

3) Holick MF. Vitamin D Deficiency. NEJM 2007; 357:266-81.

This article is provided for educational and informational purposes only and does not constitute providing medical advice or professional services. The information provided should not be used for diagnosing or treating a health problem or disease, and those seeking personal medical advice should consult with a licensed physician.  No physician-patient relationship is created by this article or its use. Neither the Advisory Council nor its employees, nor any contributor to this website makes any representations, express or implied, with respect to the information provided herein or to the its use. Dr. Wanagat is acting as an independent professional and not as a representative of the University of Washington.