Vitamin D RDA should be cut 50 percent, study finds – The San Diego Union-Tribune
The recommended dietary allowance of 800 International Units of vitamin D for bone health should be cut in half, according to a study released Sunday at the 2017 scientific meeting of the Endocrine Society.
An RDA of 400 IU of vitamin D daily is enough for 97.5 percent of the population, according to the study. The abstract can be found at j.mp/endo2017d.
Since older women generally need more vitamin D for bone health than younger people, the 400 I.U. limit would suffice for them as well.
The study states it uses newer, more accurate technology to retest samples from an earlier double-blind study of the effect of vitamin D3 supplementation, which determined that a daily RDA of 800 I.U. would protect bone health.
The original study followed 163 healthy postmenopausal Caucasian women aged 57 through 90 years. They had gone through menopause at least seven years earlier. They also had vitamin D insufficiency according to World Health Organization standards of 20 ng/ml in blood serum or lower according to what’s called an 25(OH)D or 25 hydroxy vitamin D blood test.
Both studies were performed by a team including Christopher Gallagher, M.D., director of the Bone Metabolism Unit in the Division of Endocrinology of Creighton University School of Medicine in Omaha, Nebraska.
“The RDA is easily achievable with a supplement of 400 IU in winter, when vitamin D levels are lowest in North America,” Gallagher said in an Endocrine Society statement. “This has important ramifications for public health recommendations. The amount of vitamin D needed, 400 IU daily, is less than the figure recommended by Institute of Medicine.”
Since many other diseases are affected by vitamin D deficiency, the doses needed to treat or prevent those diseases may be different, Gallagher said in the statement.
Vitamin D is a fat-soluble hormone best known for helping form strong bones and preventing rickets. In recent decades, deficiency has been linked to increased risk of cardiovascular disease; both Type 1 and Type 2 diabetes; multiple sclerosis and many other diseases.
But a consensus on the appropriate level of vitamin D intake hasn’t been reached. Since it is fat-soluble and stays in the body, large doses can be toxic. A number of experts suggest it’s safe to take up to 10,000 IU daily for long times. Toxicity has been demonstrated after taking 50,000 I.U. for several months, according to the Mayo Clinic.
There’s also some question over whether low vitamin D levels are a cause of certain diseases or whether the relationship is backwards — low levels are actually a consequence of those diseases.
For those who live in Southern California or other sunny climes, it may not be a concern. People with skin that can tan, and who expose their unprotected arms and upper bodies to the midday sun for about 5 to 10 minutes each day, can make all the vitamin D they need.
However, for those who live in less sun-drenched regions, have very dark skin or who shield themselves from the sun, supplementation may be necessary depending on diet.