麻豆传媒

New analyses from the big prospective study called cast additional doubt on the value of routine vitamin D and omega-3 fatty acid supplements for generally healthy individuals.

Daily administration of 2,000 IU of vitamin D, in many cases on top of supplements that study participants were taking on their own, had no effect on fracture risk over some 5 years, said Meryl LeBoff, MD, of Brigham and Women's Hospital in Boston, at the American Society for Bone and Mineral Research (ASBMR) annual meeting held online and in San Diego.

With virtually equal numbers of participants receiving vitamin D versus placebo, numbers of incident fractures of all types were nearly equal as well, at 769 versus 782, for a hazard ratio of 0.98 (95% CI 0.89-1.08), LeBoff said. Numbers were also very similar between groups for non-vertebral fractures and hip fractures.

And two other substudies from VITAL, both presented as "e-posters" at ASBMR by Sharon Chou, MD, also of Brigham and Women's, found no benefit from omega-3 supplements in participants' physical abilities or in biomarkers of bone health.

It's just the example of a rigorous that supplements have important preventive effects.

VITAL, you may recall, randomized some 25,000 generally healthy people, of whom about 20% were Black, in a 4×4 design to double placebo, 2,000 IU/day vitamin D₃, 1,000 mg/day omega-3 capsules, or both supplements. Median follow-up was just over 5 years. Cancer and cardiovascular events were the prespecified primary outcomes (for which ), but the design included additional substudies to examine other purported effects of these supplements.

The new analysis of fracture rates in VITAL is of particular interest because, for all the benefits claimed for vitamin D, bone health has the strongest evidence. The current government recommendation of 400 IU per day is based on studies indicating that vitamin D is necessary to maintain bone integrity.

But whether supplementation at 2,000 IU per day in addition to the normal sources -- dietary intake and sunlight exposure -- provides extra protection was less clear.

VITAL enrolled a relatively unselected group of men (ages 50 and up) and women (ages 55 and up) to receive the daily vitamin D and/or omega-3 supplements in the placebo-controlled, double-blind, double-dummy study. Participants' relatively young age (mean 67) was a point of interest for at least one member of LeBoff's audience, who questioned whether the results are relevant for older individuals, for whom fracture risk is greatest.

"We can't generalize to 80-year-olds," LeBoff acknowledged.

And vitamin D advocates could well criticize other aspects of the trial, such as the dosing (7,000 IU/day or more are often recommended) and target vitamin D blood levels.

But the results were also bolstered by the rigorous adjudication of fractures. LeBoff pointed out that the supplements were very effective in raising blood levels of the active vitamin D metabolite, 25-(OH)D, with most participants receiving the active product achieving levels of at least 40 ng/mL. (Levels of 30 ng/mL are conventionally considered adequate for bone health.)

Also, fracture rates were similar among participant groups defined by baseline levels (<20, 20-29, or ≥30 ng/mL).

In the poster presentations, Chou and colleagues explained that bone benefits have also been claimed for omega-3 fatty acids, with animal studies pointing to "increased calcium absorption, decreased urinary calcium excretion, and reduced inflammation and bone resorption."

They sought to examine the question in a VITAL subgroup, consisting of participants in the New England area who were brought in for imaging tests and physical exams. No sign of the purported benefits were seen. Measures of bone mineral density overall and at key locations, bone strength, cortical thickness, and polar stress strength index were all similar in participants receiving the active supplements versus placebo.

The same was true for physical abilities, as measured by tests of grip strength, walking speed, chair stands, balance, and other objective performance assessments.