We looked, and the evidence does not back the claim: either it was tested and did not hold up, or nobody has tested it and nothing that was tested supports it.
Biotin brings back hair lost to a biotin deficiency, which is rare. In people who are not short of it, the two small tests of biotin alone we found showed no significant gain, and doses sold for hair can make some blood tests wrong, including one used to diagnose heart attacks.
DHEA pills reliably raise hormone levels, testosterone mostly in women. In trials of older adults up to two years long, strength and quality of life did not significantly improve, and older men lost 0.9 lb of fat in a year. The prescription vaginal form is a different product.
Not on its own. In most tests, sucralose drunk alone or before a glucose drink left blood sugar where water did: 30 adults given 250 mg peaked at 126 mg/dL, against 128 on water. Some small trials found people handling sugar a little worse after weeks of it, more found no significant difference, and A1C was not significantly higher than on a dummy, water or nothing in any trial we read.
Cod liver oil's vitamin D helped end rickets. As a supplement for well-fed adults, the biggest trial of it we found, 34,601 Norwegians over a winter, half of them on cod liver oil and half on corn oil, found it did not reduce colds, other respiratory infections or Covid. The joint trials are small and split, and the vitamin A in a teaspoon ran from 40 to 4,000 micrograms across the labels we tallied.
B12 shots are a real treatment for people who cannot absorb B12. Sold for energy and weight loss to people who are not short of it, they have little behind them: in the placebo-controlled trials we found, dummy shots did about as well, and the one registered weight-loss trial we found never posted results.
Extra body fat raises inflammation markers, in genetic studies and weight-loss trials. The reverse did not hold up in the genetic studies of CRP, and anti-inflammatory drugs mostly did not take weight off: diacerein did in one small trial and two pills for psoriasis and lung disease do as a side effect, while one added 3.0 lb against a dummy pill in a 48-week trial of 286 adults with type 2 diabetes.
In the largest published trial we found, 316 of 631 adults with kidney disease were coached to drink more water for a year and drank about 20 oz more a day; among the 590 measured at the end, their top number fell half a point more than the comparison group's (both fell about 5 points), a gap that chance could explain. Smaller trials pointed both ways. What water measurably does is the opposite: a 16-oz glass raised the top number of 11 healthy volunteers, average age 57, by 11 points within the hour.
In trials that gave people coffee or none for up to 24 weeks, at up to 8 cups a day, CRP, the blood marker of inflammation most studies measure, was not significantly higher on coffee in their main comparisons. One small trial found IL-6 up 60%. Coffee drinkers in population studies tend to have slightly lower CRP. Where coffee seems to cause trouble is local: reflux in some people, and possibly gout attacks after a sudden extra few cups.
About as often as a dummy capsule does, in the trials that counted. In nearly 3,000 older hospital patients on antibiotics, 12.9% had diarrhea in the first three weeks on a probiotic and 11.7% on a dummy; in trials of healthy people, digestive complaints leaned only slightly higher, within chance. What probiotics prevent is narrower than sold, and for a few very ill people they are a real risk.
Against a dummy pill in 19,114 older adults, daily aspirin made a gap of 0.03 points a year in systolic pressure, not a significant one. Taken at bedtime, it lowered pressure in one laboratory's trials and in a 2020 pooling of mostly Chinese trials; four independent crossover trials found no significant fall.