This week, Nutrition Diva answered a few different listener questions. Here's her answer to one of them!

“Are there supplements that can prevent graying hair? I have seen some for sale on cosmetics websites and I am wondering whether there is any science behind them.”

Yes, and no. Monica checked out a half-dozen or so supplements or serums that claimed to delay the graying of hair. And many of them cited scientific studies to support their claims. But a closer look at the science left her unconvinced.

Most of the citations had to do with premature graying, that is, people who start to go gray in their 20s, and for whom early graying doesn’t run in the family. (Graying is a highly heritable trait.) Some of these cases of premature graying were eventually linked to deficiencies of certain nutrients, such as copper or B12.

However, for people who are starting to go gray in their 40s or 50s, nutrient deficiency is a much less likely explanation. Accordingly, supplementing with those nutrients isn’t likely to do much for you.

Almost all humans will eventually end up with gray or white hair (unless they end up with no hair). And this is because the production of melanin (the pigment that gives hair its color) tends to decrease with age. Some of these formulas claim to provide nutrients that are essential for the biosynthesis of melanin. Which sounds pretty scientific. But there’s a logical fallacy here.

Imagine a factory full of aging workers who can't build widgets as quickly as they did when they were younger. Bringing more and more raw materials into the factory isn't going to make your elderly workers move any faster. Similarly, loading the body up with melanin precursors won’t necessarily result in higher melanin production.

Once hair has turned gray or white, there’s really nothing you can do to restore its former color, short of dying it. So, the only thing that these products could possibly do is delay the inevitable. If you’re going gray, that will likely continue either way—and there’d be no way to know whether it might have gone quicker without the benefit of one of these supplements. But, color the Nutrition Diva skeptical.

For answers to other listener questions, check out her episode here. If you prefer to read a transcript, you can see that here.

• Savvy Psychologist discusses monogamy. Listen here.
• Curious State investigates the ransomware hunting team. Listen here.
• Project Parenthood helps teach your child to cooperate without punishments. Listen here.
• Money Girl makes your holidays less expensive (and a little more memorable). Listen here.
• Nutrition Diva gets the scoop on digestive enzymes. Listen here.
• Get-Fit Guy advises on common squat errors. Listen here.
• Modern Mentor helps you when you have a bit too much of a good thing. Listen here.
• Grammar Girl discusses the difference between "through" and "throughout." Listen here.