The Sunshine Vitamin: Are you getting enough?

The most important role of vitamin D is to preserve normal blood levels of the minerals calcium and phosphorus. With assisting minerals such as phosphorus, boron, magnesium and zinc, Vitamin D aids in the absorption of calcium, helping to form and maintain strong bones. Without vitamin D, bones can become thin, brittle or soft, and more breakable. Bone-strengthening vitamin D thereby prevents childhood rickets and adult-onset osteomalacia.

Do Americans get enough Vitamin D? Over the past few years, a growing number of scientists have come to believe we don't. The latest research even goes so far as to say that vitamin D deficiency is an unrecognized epidemic in the US.

A recent study in Boston found vitamin D deficiency in almost a quarter of adolescents tested during routine checkups who were otherwise completely healthy. Several studies have shown muscle problems and osteoporosis in adults to be strongly associated with a lack of vitamin D and pediatricians have also observed an increase in children and babies with rickets, a bone disorder caused by vitamin D deficiency. Rickets was a major health concern for children in the US until the introduction of Vitamin D fortified milk in the 1930s, but now the problem seems to be returning.

A growing body of research also suggests associations between vitamin D deficiency and a slew of more serious illnesses including multiple sclerosis and other auto-immune diseases, some cancers, cardiovascular disease, high blood pressure, rheumatoid arthritis and diabetes. Incidences of some of these illnesses are higher in populations who live further from the equator, suggesting a connection to sun exposure levels. Although these associations are more tentative, they're strong enough that scientists are pushing for a sharp increase in the recommended dose of daily vitamin D, and are also encouraging a small amount of sun exposure for the general population.

Understandably, the suggestion that people should be getting more sun has upset some dermatologists and skin cancer experts who would prefer people to have complete protection from UV rays. However, it seems possible to practice safe sun exposure by baring your face, arms and legs without sunscreen for 5-15 minutes a day, a few times a week. As commonly recommended, try to get this sun before 10:00 am and after 3:00 pm. Most researchers believe this will generate sufficient vitamin D without increasing the risk of skin cancer or wrinkling. After those few minutes though, blocking up with SPF 15 or higher is definitely recommended.

Sometimes actually catching enough rays can be difficult, especially during the winter months. There are several things that negatively affect the sun's UV ray exposure and hence decrease vitamin D. Season, latitude, time of day, cloud cover, smog, color of skin, clothing cover, indoor work, glass, and sunscreens (SPF 8 or higher) can all diminish your chances of getting enough vitamin D.

People tend to get 90% of their vitamin D from sunlight exposure, but diet is also an important way of getting vitamin D, especially for those who live in the higher northern latitudes where sun exposure is more limited. How much vitamin D should be obtained from your diet is a contentious question.

The current recommended daily amounts are:

• 5 mcg (200 IU) for people aged 19-50
• 10 mcg (400 IU) for those aged 51-69
• 15 mcg (600 IU) for those over 70

However, because the benefits and functions of vitamin D in the body have only recently begun to be investigated, how much of the nutrient is necessary for optimal health is not really known.

One cup of vitamin D fortified milk provides about one-fourth of the current estimated daily requirement in adults - although remember this requirement is possibly too conservative. Only a small number of foods, such as fatty fish and fish oils, contain naturally high amounts of vitamin D. Vitamin D supplements and multivitamins can also be taken to increase vitamin D levels.

Check this table to compare food sources of vitamin D:

Source: National Institutes of Health, adapted by Joan Bushman, MPH, RD.
** Based on 2000 calorie diet.

Be aware that because vitamin D is a fat-soluble vitamin, it is stored in the body and has the potential to reach toxic levels if taken in high doses for prolonged periods of time, particularly in supplement form. Vitamin D toxicity can cause vomiting, nausea, poor appetite, constipation, weakness, weight loss, confusion, skin rash, headaches, muscle weakness, calcium deposits and kidney stones. Prolonged sunlight exposure does not cause buildup of vitamin D as the body down-regulates its production when body levels are adequate - but it's not good for your skin!

Also be mindful that some things interfere with vitamin D absorption from foods, including mineral oil, antacids, cortisone, liver and gall bladder disorders, and some cholesterol lowering drugs.

Infants. Vitamin D supplements are often recommended for exclusively breast-fed infants because human milk may not contain adequate vitamin D. Mothers who have limited sun exposure and who are exclusively breastfeeding their infants should consult with their doctor.

Children and adolescents who consume few vitamin D food sources or who spend a lot of time indoors are at a higher risk for weakened bones and stunted growth. This can make them vulnerable to fractures and osteoporosis in later life.

People over the age of 50. As we age, the ability of skin to convert vitamin D to its active form decreases. Additionally, the kidneys, which help change vitamin D to its active form, sometimes do not work as well with aging.

Menopausal and post-menopausal women are also at greater risk for osteoporosis. During menopause the estrogen balance is changed resulting in more bone being broken down than rebuilt. Vitamin D, in addition to calcium, is a vital nutrient during this time.

People who are obese. Jacobo Wortsman, MD, and co-authors compiled a study that indicated that in the obese body, vitamin D might be stored differently than in the lean body. They speculated that with obesity, the increased fat stores remove the vitamin D from the bloodstream where it otherwise would be available for use.

People with digestive problems. Individuals who have reduced ability to absorb dietary fat may need extra vitamin D because it is a fat-soluble vitamin.