Newsbriefs: Vitamin D; Red meat and CVD risk; Psyllium and constipation

MAJOR FINDING: Vitamin D Supplements Do Not Prevent Major Diseases

Virtually every tissue in the body has receptors for vitamin D. This fact led to the hypothesis that maintaining adequate vitamin D levels might be helpful for multiple health conditions. Screening to check blood levels of vitamin D has become common and an estimated one third of U.S. adults 60 years of age or older take vitamin D supplements (not even counting multivitamins or other compounds containing vitamin D).

A large, well-designed, randomized controlled trial called VITAL (Vitamin D and Omega-3 Trial) has produced results that may change all that. VITAL randomly assigned nearly 26,000 U.S. adults 50 years of age and older to one of four groups: vitamin D3 (2,000 International Units per day)plus omega-3 fatty acids (1 gram per day); vitamin D3 plus placebo; omega-3 fatty acids plus placebo, or double placebo. The results showed that vitamin D supplementation did not prevent cancer, cardiovascular disease, or falls, improve cognitive function, reduce atrial fibrillation, change body composition, reduce migraine frequency, improve stroke outcomes, decrease age-related macular degeneration, or reduce knee pain.

Now, another analysis from the study reports that, contrary to expectations, supplementation with 2,000 IU of vitamin D3 also did not reduce the risk of fractures during the more than five-year follow-up period, whether or not calcium supplements were used.

Importantly, the results of the VITAL study found that even people considered vitamin D deficient (blood levels less than 20 nanograms per milliliter) did not benefit from taking vitamin D supplements.

These important findings are consistent with the latest recommendations from the U.S. Preventive Services Task Force, which no longer recommend vitamin D or calcium supplements for the general population.

Red Meat Associated with Increased CVD Risk Through the Gut Microbiome

A recent study by Tufts researchers and colleagues looked at the dietary habits of nearly 4,000 participants aged 65 and older and measured the level of specific metabolites in their blood. Atherosclerotic cardiovascular disease (ASCVD) events—like heart attacks and strokes—were recorded over 12.5 years follow-up.

After adjusting for sociodemographic factors, lifestyle, and dietary factors, higher intake of red meat was associated with higher risk of ASCVD. Intakes of fish, poultry, and eggs were not significantly associated with risk. The study then looked at participants’ blood levels of metabolites (byproducts) that are known to be synthesized by gut bacteria. These included TMAO (trimethylamine N-oxide), an end-product of the breakdown of L-carnitine, a molecule found in red meat and other animal foods, and other related metabolites. In this study, people who regularly consumed more red meat, but not fish, poultry, and eggs, had higher levels of TMAO in their blood. Analysis suggested that TMAO and other metabolites that result from gut microbes breaking down L-carnitine may play a larger role in meat-ASCVD associations than blood pressure or blood cholesterol levels.

This study highlights one important way high intake of red meat may increase risk for cardiovascular disease, supporting the idea that our gut microbiota and the metabolites they generate from the foods we eat are key players in our health.

Psyllium Fiber May Relieve Chronic Constipation

If you are constipated, dietary fiber and fluid intake may help. For those who suffer from chronic constipation, fiber supplements may be necessary. A review of 16 randomized controlled trials concluded that supplementation with psyllium fiber improves constipation. Overall, 66 percent of participants responded to fiber treatment. The fiber increased stool frequency and consistency, but also increased flatulence (passing gas) compared to control.

The ground-up husk of Plantago ovata seeda, psyllium is a soluble fiber. Soluble fiber forms a gel with liquid that helps make stools softer and adds bulk that triggers intestinal contractions. Supplements come in coarse or fine powders or in capsules. Powders are mixed into water or juice and may be flavored or plain. The optimal amount depends on a number of factors, so read package labels for dosing information.

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