GOOD NIGHT SLEEP PROTECT FROM PROSTATE CANCER

A good night's sleep, the prescription for many ills, could protect against the development of prostate cancer, the findings of a new study suggest.

Researchers from the United States and Iceland found that higher levels of melatonin in men's morning urine were associated with a decreased risk for prostate cancer, particularly advanced disease.

Melatonin is a hormone that is produced exclusively at night. Higher levels have been tied to longer, more restful sleep.

"These data provide support for the influence of the circadian rhythm in prostate carcinogenesis," conclude the authors, led by Sarah C. Markt, MPH, a doctoral candidate in the Department of Epidemiology at the Harvard School of Public Health in Boston.

However, the results need to be replicated in a larger study, Markt told Medscape Medical News in an interview.

The study was presented at the American Association for Cancer Research (AACR)-Prostate Cancer Foundation Conference on Advances in Prostate Cancer Research in San Diego last week.

This connection between melatonin and prostate cancer did not come out of left field, said an expert not involved in the study.

"The association between melatonin and cancer has been observed in other cancer types as well. Research on melatonin and cancer dates back several decades," June M. Chan, ScD, professor of epidemiology & biostatistics and urology at the University of California, San Francisco, said in an email.

In their study, researchers from Harvard and the University of Iceland in Reykjavik retrospectively conducted a nested case–cohort analysis of 928 Icelandic men enrolled from 2002 to 2009 in a larger public health study.

Of the 928 study participants, 111 men were diagnosed with prostate cancer (24 with advanced disease). The diagnosis of prostate cancer was ascertained by linking the cohort to the nationwide Icelandic Cancer Registry.

When the men were initially recruited, the Icelandic researchers collected urine samples from their first morning void and asked participants to complete a questionnaire about sleep patterns.

Subsequent lab work examined, among other things, urine levels of the main byproduct of melatonin, 6-sulfatoxymelatonin.

The median level of 6-sulfatoxymelatonin in the study participants was 17.14 ng/mL of urine. Men who reported in the questionnaire that they took medications for sleep, had problems falling asleep, or had problems staying asleep had significantly lower levels of 6-sulfatoxymelatonin than men without sleep problems.

The researchers then looked at the relation between 6-sulfatoxymelatonin level and prostate cancer.

Men with 6-sulfatoxymelatonin levels higher than the median had a statistically significant borderline decreased risk for prostate cancer overall (hazard ratio [HR], 0.69; 95% confidence interval [CI], 0.44 - 1.08).

More notably, men with levels higher than the median had a significant 75% reduced risk for advanced disease, compared with men with levels lower than the median (HR, 0.25; 95% CI, 0.08 - 0.80).

In short, the men with above-average melatonin levels had a reduced risk for prostate cancer.

Markt pointed out that Iceland is a geographically extreme country. She witnessed the very long days and very short nights when she visited in the summer months.

In the cohort survey of the Icelandic men, 1 in 7 reported problems falling asleep, 1 in 5 had problems staying asleep, and about 1 in 3 used sleep medications.

However, any difference in sleep problems between, say, American and Icelandic men should not change the relation between melatonin levels and prostate cancer that was seen in the study, Markt explained.

Dr. Chan noted that it is "unclear just from the abstract alone what other risk factors were considered in conjunction with melatonin levels" in the study.

Exercise, vitamin D levels, and other factors could have acted as confounders and partially explained the observed association between prostate cancer and melatonin levels, she told Medscape Medical News.

Nevertheless, Dr. Chan called the study findings "provocative," and noted that night-shift employment has been associated with an increased risk for various cancers in men.

Should men concerned about their risk for prostate cancer take melatonin supplements? "I think these data are pretty early to suggest that men should take melatonin supplements solely for prevention of prostate cancer," said Dr. Chan.

The study was funded by the Harvard Catalyst. Ms. Markt and Dr. Chan have disclosed no relevant financial relationships.

AACR-Prostate Cancer Foundation Conference on Advances in Prostate Cancer Research. Presented January 20, 2014.