How much vitamin D is enough?

In a new study, researchers suggest that when recommending vitamin D supplements, doctors should look at each individual patient as having different requirements and not rely on “one-size-fits-all” guidelines.

The study highlights the need to gain consensus through improved tests for vitamin D levels that are currently available.

The research was conducted by a team from Rutgers University’s New Jersey Medical School.

Vitamin D’s main function is to help the body absorb calcium.

Deficiency can cause delayed skeletal development and rickets in children and may contribute to osteoporosis and increased risk of fracture in adults.

Vitamin D supplements work best when taken with calcium for rickets and bone loss that occurs with aging.

According to the Institute of Medicine, people with less than 20 nanograms of vitamin D per milliliter of blood are deficient.

The Endocrine Society sets a higher threshold of 30 nanograms. Neither guideline is currently more definitive than the other.

Elderly people who are vitamin D deficient benefit from supplementation as protection against fracture.

However, studies did not show supplements to be beneficial as protection against a fracture if the elderly person was already sufficient in the vitamin.

Further, more vitamin D supplementation is not better. Previous studies have shown that very high doses of vitamin D (300,000–500,00 iu taken over a year) seem to increase fracture risk.

The researchers say that recommendations based on earlier studies using a number of different tests for vitamin D levels persist and current guidelines vary.

The National Academy of Medicine recommends 400 iu/day for infants, 600 iu/day for people age 1 to 70, and 800 iu/day for people over 70. The Endocrine Society suggests doses up to 2,000 iu/day for adults.

Although vitamin D supplementation has been shown to reduce overall mortality and some studies suggest that vitamin D might be beneficial for immune function, cancer, and cardiovascular health, a consistent benefit of vitamin D supplementation has yet to be shown.

It is also not clear that the most optimal levels for vitamin D are the same for Caucasians, blacks, or Asians alike.

More laboratories are now implementing improved tests and efforts are being made to standardize results from different laboratories.

The lead author of the study is Sylvia Christakos, a professor at Rutgers University’s New Jersey Medical School.

The study is published in the journal Metabolism, Clinical and Experimental.

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