Melatonin is safe to take daily
DEAR DR. ROACH: In a recent column, you responded to a reader asking about the link between Benadryl and dementia, and near the end you mentioned that melatonin is "very safe." I've heard that taking melatonin can affect your body's natural production of melatonin, causing a loop -- the more you take, the less your body will produce -- thus necessitating a person to continue taking it indefinitely. Would you speak to this? -- L.P.
ANSWER: Many hormones do have what is called a feedback loop, where high blood levels of the hormone will prevent the body from making more. That is the case, for example, with thyroid hormone. High levels of thyroid hormone, whether made by the body or taken as a medication, will shut off production of more thyroid hormone, preventing excess. However, if you stop taking thyroid hormone, the body will sense this and restart production of thyroid hormone. In some cases, it takes a period of time to restart synthesis, during which the body has low hormone levels.
This does not appear to be a major issue with melatonin, which has a very short lifetime inside the body, and whose secretion is largely regulated by the length of daylight. As such, it is less likely than other treatments to cause a "rebound" -- a worsening of insomnia after stopping it. However, the situation is complex, and some people certainly might notice such an effect. It is also true that melatonin levels tend to decrease with age.
Melatonin, at low dose -- such as 0.5 to 1 mg -- is indeed thought to be very safe. There are no perfectly safe substances: Anything can be dangerous at the right dose. Headache, confusion and fractured sleep have been reported in people taking melatonin at doses up to 36 mg.
DEAR DR. ROACH: We know that human urine has healing benefits to the body. If you are camping and get a bad gash, would your urine help heal it? -- V.Z.
ANSWER: I have increasingly read that some people believe in the healing powers of urine, but I am not one of those people. There is no good scientific evidence of any beneficial power of urine. Urine is a waste product.
In the case you mention, cleaning and covering the wound is key. Campers should bring a first-aid kit (it doesn't need to be big or heavy) and use clean water (drinking water is fine) to irrigate the wound as best as possible then dress it, and get to definitive help as soon as possible.
DEAR DR. ROACH: Our son is a runner. He is in good health, and runs 30-, 50- and 100-mile races on various terrains. We are concerned about the distances. Is this a healthy activity? -- T.E.
ANSWER: I don't have a definitive answer for you, as the medical literature is unclear and there are people with strong opinions on both sides.
On the one hand, ultramarathoners are exceptionally healthy people, and they have lower rates of illness than expected. However, it's not clear whether that's just because of their running: It could be that only superbly healthy people take up running those distances.
There is some evidence that very high levels of exercise may cause heart damage both in the short and long term: I have talked to experts who disagree, but a recent study confirmed this. What is clear is that one can get a great deal of benefit from much less exercise than your son is doing.
People like your son tend to be passionate about their running, and I don't try to talk them out of it.
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 request an order form of available health newsletters at 628 Virginia Dr., Orlando, FL 32803. Health newsletters may be ordered from www.rbmamall.com.
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