DEAR DR. ROACH: My 78-year-old father is experiencing the early signs of dementia. It has been suggested that he try a $500 device that would aim a low-intensity red LED light into his nose to stimulate his brain and stabilize or perhaps even reverse the symptoms of dementia. On the surface, it seems like a modern version of snake oil designed to separate desperate people from their money, but I am open to the idea if it might be an effective treatment. An internet search suggests that there have been limited clinical trials that have shown hopeful results, but some of the trials have been sponsored by the company selling the device. Is there any tangible evidence to suggest that photobiomodulation reduces the symptoms of dementia? -- R.C.

ANSWER: The theory in light therapy is to reduce cell damage and death by reducing plaques inside neurons that are the hallmark of Alzheimer's disease. There have been some provocative trials (small and relatively short), but in my opinion there needs to be more data before I'd feel comfortable recommending purchasing a device. The trials have not shown significant toxicities, however, and low-intensity red light is probably safe.

DEAR DR. ROACH: I am a 76-year-old retired registered nurse in reasonably good health. I am moderately obese. I have experienced cardiac irregularities since going through a stressful time 40 years ago, including benign premature ventricular contractions. I have also experienced periods when my heart seems to flutter. Twenty-four hour heart monitors have not revealed any abnormalities. For the past couple of years, my resting heart rate has been falling. Twenty years ago, it was about 72. Now, according to my smartwatch, it's falling pretty consistently into the low 40s, occasionally the high 30s. This is during sleep. I have double-checked the watch's accuracy multiple times, and it appears to be very accurate. I have exhibited no symptoms, but I'm concerned that the rate continues to decline. The doctors don't want to do further testing because I am asymptomatic. Please advise if you concur that this is the right approach or if I should be concerned. -- S.L.

ANSWER: Slow heart rates are common during sleep, and in the case when people are truly without symptoms, usually they do not need treatment. However, I am concerned about two issues.

The first is that you have had some symptoms of the flutter sensation. While this is not the typical lightheadedness, especially upon standing, you aren't really symptom-free. Heart rates in the 30s usually have symptoms, although some people compensate so well through the body's ability to adapt that they only notice the symptoms when they feel much better after treatment. I suspect that there is a reasonable likelihood you will need a pacemaker in the future.

The second concern is that slow heart rates during sleep should make a physician think about the possibility of obstructive sleep apnea, especially in a person who is overweight. You should consider a sleep study, especially if you feel sleepy during the day, have morning headaches or snore.

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.