Does an elevated melatonin level in morning urine really reduce risk for prostate cancer?


Every so often you come across something so far  “out of left field” that just possibly it may make some sense. So having said that, let me declare my ignorance.

Although I am aware of the unproven hypothesis that increased ambient light at night in cities and towns is a potential cause of cancer (which I have a very hard time believing), I have never heard of:

And so from way out in left field (at least for me) comes a paper by Alpert et al. suggesting the possibility that certain, specific light wavelengths may lower melatonin production and thus increase risk for some forms of cancer.

According to Alpert and colleagues, “For more than 15 years evidence has been accumulating that there is a link between a lack of melatonin and cancer, especially breast, ovarian and prostate cancer.” (This is in fact true, see for example the summary of research by Larsen.)

They continue by stating, “For a similar period it has been known that exposing the eyes to light when melatonin is normally flowing reduces or eliminates the flow. What is relatively new is that it is primarily the blue wavelengths that are responsible for loss of melatonin. Blocking these blue rays with amber glasses restores melatonin flow.”

They then tell us that the abovementioned “direct evidence” from analysis of “the famous nurses’ health study” links a higher than normal level of melatonin in first morning urine to a reduction in the incidence of breast cancer.

From here the authors present the hypothesis that “wearing amber glasses (or using blue-free light bulbs) for a few hours before bedtime maximizes melatonin production and reduces the risk of breast, ovarian and prostate cancer and possibly other cancers.”

While I consider this hypothesis to be “out of left field,” I do not necessarily consider it to be bizarre.

Proving (or disproving) this hypothesis may be difficult, however:

  • At what age would one need to start wearing amber glasses or avoiding blue-free light bulbs to lower one’s prostate cancer risk?
  • How much exposure to blue light can negate the accumulated benefit of evening blue-free light?
  • Is there a morning urine melatonin level that can be associated with (say) a 75 percent reduction in risk for prostate cancer?
  • And again, how many days of failure to achieve that morning urine melatonin level could negate a month’s worth of achievement of that morning melatonin level?
  • Since melatonin is available over the counter and can be taken orally, would a simple dose of melatonin at night be able to stimulate comparable risk reduction? That would be a much easier clinical trial to conduct (and has the potential added benefits of improving sleep patterns and lowering risk for essential hypertension).

Other comments on this hypothesis will be welcomed.

Finally, one word of warning. According to the American Council on Science and Health, certain populations should not undertake melatonin therapy. These include:

  • People with autoimmune diseases, like rheumatoid arthritis (because high doses of melatonin may worsen such conditions)
  • People taking steroid medications (because melatonin may counteract their therapeutic effects)
  • People taking monoamine oxidase (MAO) inhibitors

2 Responses

  1. Was going to say that “melatonin level in morning urine” is an impossibility. But I see that you didn’t invent that; you’ve linked to a paper entitled “Urinary Melatonin Levels and Postmenopausal Breast Cancer Risk in the Nurses’ Health Study Cohort”. Gosh. Anyway, there isn’t melatonin in urine, but melatonin levels can be tracked by measuring, in urine, the major metabolite of melatonin through the morning/day. They explain that in their text, but I really don’t like the implication in their title or yours.

    Yes, it is short wavelength (about 480 nm) light to the eyes which banishes melatonin. And blue-blocking (amber) goggles allow one to see in the evening without stopping melatonin production. But it’s not a good idea to convince the system that nights are many hours longer than they really are; that leads to depression. Allowing the secretion of melatonin as early in the evening as it “wants” may be a good idea, but plenty of light on awakening is needed for balance.

    For the record, what I know about melatonin is in relation to my interest is in the field of circadian rhythms, not cancer prevention.

    Note, too, that melatonin is available over-the-counter in the USA and Canada, but is prescription-only or unavailable in other countries.

  2. Thanks for the additional clarifications. For clarity, let me just say that I would want a LOT more information before suggesting that we had convincing evidence of the effectiveness (or safety) of melatonin use to prevent any form of cancer.

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