Check for conflicts of interest from sources of information

Dear Dr. Roach: I have been reading a lot about the cardiovascular and general health benefits of supplemental vitamin C and lysine given that human beings are the only animal that does not produce vitamin C.

I also read that otherwise healthy adults should be taking 4,000 milligrams of vitamin C and 2,400 milligrams of lysine, with adults suffering from cardiovascular disease taking up to 6,000 milligrams of vitamin C daily. What do you think about this? — B.S.

Answer: I disagree with the sources you have been reading. Humans and primates do need dietary vitamin C, but so do some birds, fruit bats, guinea pigs, coho salmon and other species, which also are unable to make it. More importantly, large trials — such as the Physician’s Health Study II, which randomly assigned nearly 15,000 men to vitamin C versus placebo — found no significant difference in heart disease, cancer or death rates.

Foods high in vitamin C, including many fruits and vegetables, help reduce heart disease risk, but supplements have not been proven to do so.

Lysine (along with arginine, another amino acid) reduced anxiety levels in one study, but there is no good evidence that it reduces heart disease risk.

When reading medical sources, be sure to look for any potential conflicts of interest.

Some of the online sources I found on this subject were selling the very same supplements they were recommending. It’s also important to look for current evidence; some cited studies are from the 1950s.