Health Support Supplements: 6 With Evidence, Ranked With Doses

Soluble fiber binds bile acids and slows glucose absorption; fermentable fiber feeds the gut bacteria that produce short-chain fatty acids. The Lancet series by Reynolds and colleagues pooled 185 prospective studies and 58 trials and found that people eating 25 to 29 g per day had 15 to 30 percent lower all-cause and cardiovascular mortality than those eating the least, with trials confirming lower LDL, blood pressure and body weight. Most adults on a typical Western diet eat well under 20 g. A psyllium supplement of 5 to 10 g closes part of the gap; oats, beans and vegetables close the rest.

Vitamin D is made in skin under UVB and is low in a large share of people who train indoors, live at northern latitudes or have darker skin. Owens and colleagues review the athlete data: deficiency impairs muscle function and immunity, and correcting it with 1,000 to 2,000 IU per day restores both. The larger claims fail in trials. VITAL (Manson 2019) randomized 25,871 adults to 2,000 IU or placebo for a median 5.3 years and found no reduction in invasive cancer or major cardiovascular events.

The testosterone claim fails too: a randomized trial in men with low testosterone found no androgen increase from vitamin D (Lerchbaum 2019). Test first; supplement to a blood level of 75 nmol/L (30 ng/mL); stop chasing higher numbers.

Magnesium is a cofactor in more than 300 enzymes including those of ATP metabolism, and dietary intake is below the recommended 400 to 420 mg for many men. Zhang and colleagues pooled 34 randomized trials (2,028 people) and found supplementation lowered systolic pressure by about 2 mmHg and diastolic by 1.8 mmHg at a median 368 mg per day, with larger effects in people with low starting levels. Glycinate and citrate are well absorbed; oxide is poorly absorbed and mostly laxative. The supplemental upper limit is 350 mg because more than that causes diarrhea, not because of toxicity.

EPA and DHA lower triglycerides in a dose-dependent way and are incorporated into cell membranes, which is the basis of the anti-inflammatory claim. On hard outcomes the two best summaries disagree at the margin: the 2020 Cochrane review (Abdelhamid, 86 trials) concluded that omega-3 supplements have little or no effect on all-cause mortality or stroke, while Hu and colleagues' meta-analysis of 13 trials found modest reductions in heart attack and coronary death that grew with dose. A reasonable reading is a small cardiovascular benefit at 1 to 2 g of EPA plus DHA per day for people who eat little fish, and no benefit for longevity in general.

Zinc is required for T-cell function and hundreds of enzymes; Prasad's review documents how even mild deficiency impairs immunity and how repletion restores it. Heavy sweating and low meat intake raise the risk of low zinc in athletes. What zinc does not do is raise testosterone in men who are not deficient: Wilborn and colleagues gave ZMA (zinc, magnesium, vitamin B6) to trained men for eight weeks and found no change in anabolic hormones, strength or body composition versus placebo. Long-term intake above 40 mg per day impairs copper absorption.

N-acetylcysteine supplies cysteine for glutathione synthesis, which is why it is the antidote for acetaminophen overdose and a mucolytic in lung disease; Rushworth and Megson review these established uses and the speculative ones. There is no outcome trial showing that NAC protects the liver of a healthy adult, and its antioxidant action has been reported to blunt some of the adaptive signaling from training. It is not dangerous at 600 to 1,200 mg, but it is a treatment without a condition for most buyers.