University Times

New guidelines from the Institute of Medicine (IOM) recommend that taking 600 international units (IUs) of vitamin D per day is sufficient for most people, while people over age 70 need 800 IUs daily to maintain bone health.

The vitamin helps the body absorb calcium and is important in protecting against rickets and osteoporosis. According to the National Institutes of Health (NIH), the vitamin also modulates cell growth and plays a role in neuromuscular and immune function and in reducing inflammation.

So, how can we be sure to get enough vitamin D? Some can be gained through sunlight and food sources, but most people probably need vitamin D supplements to meet those recommendations, experts say.

Vitamin D is found in fatty fish, such as salmon, mackerel and tuna; fish liver oils are good natural dietary sources of vitamin D. Small amounts also are found in liver, egg yolks and cheeses.

Milk, baby formula and other foods (such as yogurt, cereals, margarine and orange juice) often are fortified with vitamin D.

Vitamin D also is produced naturally in response to ultraviolet (UV) rays from sunlight. However, many people don’t spend enough time outdoors and merely sitting near a sunny window inside is ineffective; the UV rays can’t pass through glass.

The body can store the vitamin D it produces, but that supply can be depleted during the winter months — particularly for people who live far from the equator, causing seasonal variations in vitamin D levels.

According to NIH, some research suggests that getting up to a half-hour of sun exposure at least twice a week between 10 a.m. and 3 p.m. typically is sufficient, but many factors influence the amount of vitamin D that is produced. The season, time of day, cloud cover, use of sunscreen and skin pigmentation (dark-skinned people need more sun to generate the same vitamin D levels as lighter-skinned individuals) all impact the production of vitamin D.

The need for supplements

“No way” can people get sufficient vitamin D in their diet, said nutritionist Leslie Bonci. To get the 800 IUs of vitamin D recommended for older adults, a person would need to have eight egg yolks or eight glasses of milk or fortified orange juice every day.

“From a calorie perspective, it just won’t work,” said Bonci, director of sports nutrition at the UPMC Center for Sports Medicine.

Foods fortified with vitamin D contain a maximum of 100 IUs, so she recommends that people take a vitamin D supplement.

Finding a 600 IU supplement may be difficult. More often, supplements are 1,000 IUs or 2,000 IUs.

“At a minimum, 1,000 IUs is fine,” Bonci said, adding that for most people, taking more “probably isn’t necessary.”

Shoppers may see vitamin D2 and D3 on store shelves. Bonci said either is fine because there is little difference in how the body absorbs vitamin D2 (which is made from yeast) and vitamin D3 (which comes from animal sources).

Likewise, she said, there’s no need to seek out brand-name vitamin D products.

Know your numbers

Bonci said it’s important for people to be aware of how much vitamin D they get on a daily basis.

“People need to know their numbers” — not only in terms of how much vitamin D they take daily, Bonci said, but also in terms of blood levels of vitamin D.

Vitamin D levels are checked using a test that measures the level of 25-hydroxyvitamin D, or 25(OH)D, in the blood. The IOM found that blood levels of 20 nanograms per milliliter indicates sufficient vitamin D intake.

“You need to know your serum level,” Bonci said, adding that testing is not routine.

That’s something to discuss with your health care provider, she said.

Calcium supplements often contain vitamin D to boost calcium absorption, she noted, adding that some supplements are being reformulated to reflect the IOM recommendations.

“Go down the checklist of all your current supplements,” she said, then learn your blood serum level.

Citing research indicating the vitamin’s potential role in protecting against prostate cancer, multiple sclerosis, falls and depression, Bonci said, “You might take it for bone health, but it also might have a head-to-toe benefit.”

—Kimberly K. Barlow