DEAR DR. ROACH: I have always been a proponent of the attitude that “no matter how much you make yourself look younger on the outside, you are still aging on the inside.” I read a recent article on the benefits of the supplement NAD+, which describes the inside anti-aging benefits. It appears that there are quite a few. I am very interested in your take on this. — K.R.

ANSWER: NAD+ is a coenzyme that is critical for basic function of the cell. One major function is in the energy-producing cycles in the mitochondria.

ATP is the basic energy currency of the cell. NAD+ is reduced back to NADH in a process called oxidative phosphorylation. This process produces energy in the form of ATP. A certain amount of NAD+ is needed for the system to work, and adding more is not necessary. However, NAD+ and NADH have many more jobs, in and out of the mitochondria.

It is true that as animals age – both mice, and to a lesser extent, humans have been studied – NAD+ levels tend to decrease. This seems to relate to increased destruction of NAD by the cell. Raising NAD+ directly requires intravenous supplementation, but there are NAD+ donors, such as nicotinamide riboside, that will increase NAD+ levels when given orally. Trials in mice have shown some benefits in cellular function, such as improved ability to metabolize sugar. There is not yet any good evidence that NAD+ supplementation in humans leads to any clinical benefit. Studies are ongoing, and nicotinamide riboside may be useful in treatment of some diseases.

However, there is evidence that while NAD+ may help mitochondria in our cells (a potentially “anti-aging” effect), it may also increase cancer cell growth. Studies in mice have shown increased rates of developing pancreatic cancer in mice genetically predisposed to do so.

Finally, supplements are not regulated by the Food and Drug Administration to the same levels that pharmaceutical drugs are, and there is no guarantee that any supplement you are taking, such as nicotinamide riboside, has an accurate amount listed on the bottle.

Although I would love to be proven wrong, I don’t think that NAD+ is the “fountain of youth” as some of its supporters have touted. I don’t recommend taking the supplement until much more information is available about the benefits and risks of long-term use. When a person is taking a drug or supplement to prevent disease, and they have no symptoms to treat, the evidence needed to prove benefits outweigh risks needs to be very strong.

DEAR DR. ROACH: Do people develop fewer colds as they age? If so, why? I’m 78 and haven’t had a cold for at least 25 years. – J.S.B.

ANSWER: It is true that older people usually have fewer colds as they age, but that is largely due to being exposed less frequently. The immune system also is likely to have been exposed to many more viruses as we age, but unfortunately, for some viruses, one can never get high-level immunity to; others have so many different strains that it’s likely you will get exposed to one your immune system doesn’t know.

Dr. Roach regrets that he is unable to answer individual letters, but will incorporate them in the column whenever possible. Readers may email questions to ToYourGoodHealth@med.cornell.edu or send mail to 628 Virginia Dr., Orlando, FL 32803.