High doses of vitamin D fail to boost calcium absorption, bone mineral density, study finds

By Elizabeth Crawford contact

- Last updated on GMT

High doses of vitamin D fail to boost calcium absorption, study finds

Related tags: Bone mineral density, Vitamin d

High doses of vitamin D are no more effective than a placebo at improving muscle function and preventing falls and fractures in older adults who are deficient, according to recently published research that will weigh heavily in the ongoing debate about how much vitamin D is enough. 

The study, published Aug. 3 in JAMA Internal Medicine, found giving postmenopausal women deficient in vitamin D high enough doses of cholecalciferol for a year to maintain their levels at 30 ng/mL “had a negligible effect on calcium absorption and no clinically meaningful beneficial effects on [bone mineral density], muscle function or falls” ​when compared to women who received lower doses of vitamin D or a placebo.

The results of the 221-woman study contradicted researchers’ hypothesis that a higher dose would elevate women’s vitamin D serum to a level that would help protect against osteoporosis by increasing total fractional calcium absorption and bone mineral density more than a low-dose of vitamin D or placebo would.

The high dose increased absorption only 1% compared to 1.3% for the placebo arm, according to the study. It also found no meaningful differences between changes in the groups’ bone mineral density, muscle mass or muscle control.

“Likewise, we found no between-arm differences for numbers of falls, number of fallers, physical activity or functional status,” ​write the researchers, who were led by Karen Hansen at the University of Wisconsin School of Medicine and Public Health.

With this in mind, they write the “study results do not justify the common and frequently touted practice of administering high-dose cholecalciferol to older adults to maintain”​ vitamin D serum levels of 30 ng/mL or greater.

Rather, they say, the results support the Institute of Medicine’s conclusion that vitamin D repletion occurs at a lower vitamin D serum level of 20 ng/mL or greater.

Is less vitamin D enough?

The findings come as a blow to proponents of high-dose vitamin D supplementation to protect deficient patients against osteoporosis-related injuries.

In an accompanying editorial, Deborah Grady, a professor of epidemiology and biostatistics and medicine, takes the study’s conclusion one step further. She argues: “These data provide no support for use of higher-dose cholecalciferol replacement therapy or indeed any dose of cholecalciferol compared with placebo.”

She adds that the study is “informative”​ in the “ongoing controversy regarding the definition of vitamin D insufficiency and the optimal treatment goal,”​ because it tested various dose-strengths in deficient older women who were otherwise healthy and did not have osteoporosis.

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This study was designed to mislead.

Posted by Abraham Safirstein,

Where did they get the pathetic idea that a level of 30 ng/mL is the goal? The bare minimum should be 50 ng/mL and taken together with vitamin K2, otherwise it is like giving a baby aspirin to an adult's headache and then saying that aspirin is useless. The real target should be a level between 60 and 90 ng/mL, and then we will see if it works or not.

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Poor trial design

Posted by William B. Grant,

It was a poorly-designed study. The authors should have read the paper below, then enrolled women with low, not average, vitamin D levels. although the study found slight increases in bone mineral density, the increase would have been significant if women with low vitamin D levels had been studied.

Kuchuk NO, van Schoor NM, Pluijm SM, Chines A, Lips P. Vitamin D status, parathyroid function, bone turnover, and BMD in postmenopausal women with osteoporosis: global perspective. J Bone Miner Res. 2009;24(4):693-701.

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Waste of time and money

Posted by Pete Granger,

This type of research is a complete waste. If one is attempting to establish optimal calcium distribution and absorption in humans it cannot be done in isolation of vitamin K status. When are researchers going to comprehend this simple fact? The bulk of research suggests humans probably get by on lower calcium intake than recommended - especially if provided in bioavailable dairy form, in combination with a modest intake of both vitamin D and vitamin K. Vitamin D from sunshine or supplements, vitamin K from parsley, greens or supplements. Calcium supplements should not be taken, especially in combination with a depleted vitamin D and K status. In this later instance calcium may be distributed where you do not want it to be.

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