Food for thought--is the beneficial effect of exercise due to melatonin

The beneficial effect of exercise reported at last year's ASCO meeting was most marked in estrogen receptor positive breast cancer patients (her2 status was not delineated as I recall). It was hypothesized that exercise might decrease estrogen secretion, but this has not in the past been found to be the case in non breast cancer patients doing only moderate exercise, which was what this study explored.

It has recently been postulated that the effect might be due to variation in melatonin production/secretion. Here is the relevant abstract hot off the "press":


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1: Am J Epidemiol. 2005 Dec 1;162(11):1114-22. Epub 2005 Oct 5. Related Articles, Links

Light and exercise and melatonin production in women.

Knight JA, Thompson S, Raboud JM, Hoffman BR.

Prosserman Centre for Health Research, Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada.

Melatonin may protect against breast cancer. Light and other factors influence melatonin, but the evidence is limited. The authors conducted a study to determine factors related to melatonin. Women volunteers recruited in Toronto, Canada, from 2002 to 2004 collected urine for three nights (winter and summer), took periodic light measurements, and recorded exposures in a diary. The relation of each variable to log-transformed creatinine-corrected 6-sulfatoxymelatonin in overnight urine was determined by use of generalized estimating equation linear regression. The final model was based on 1,054 measurement days from 213 participating women. None of the light variables was related to the log of 6-sulfatoxymelatonin. A significant interaction between season and day length was included in the final model. The most significant factor was duration of exercise (beta = 0.072; p = 0.004, two-tailed), which increased the amount of melatonin produced. Exercise duration later in the day was more significant (beta = 0.108; p = 0.0009, two-tailed). There was no difference between moderate or strenuous exercise. The failure to find a relation between light brightness and melatonin may be due to the difficulty of measuring this, as well as the importance of the light spectrum, which could not be measured. It is possible that the protective effect of exercise with respect to breast cancer may operate in part through an effect on melatonin.

PMID: 16207802 [PubMed - in process]

Good find.

Fascinating.

RB