Sedentary behaviour has unclear link with prostate cancer risk

By Joanna Lyford, Senior medwireNews Reporter

Sedentary behaviour is not a clearcut risk factor for prostate cancer, analysis of a large population-based cohort indicates.

Despite failing to demonstrate an association between activity levels and this form of cancer, the researchers say that such a link remains biologically plausible and worth exploring in future studies.

The study was led by Brigid Lynch (Baker IDI Heart and Diabetes Institute, Melbourne, Victoria, Australia) and used data from the National Institutes of Health–American Association of Retired Persons Diet and Health Study.

The cohort comprised 170,481 men who were assessed at baseline in 1995–6 and followed-up for an average of 8.5 years. During this time there were 13,751 incident cases of prostate cancer. The men’s median age at diagnosis was 69.5 years.

In the primary analysis, Lynch et al found no significant correlation between self-reported daily sitting time and risk of any prostate cancer, advanced prostate cancer or prostate cancer mortality.

Nor were there correlations between men’s self-reported time spent watching television or videos and any prostate cancer measure.

Further analysis revealed a significant interaction between television/video viewing time and body mass index (BMI), report the authors. Accordingly, they repeated their analyses after stratifying men into normal, overweight and obese categories.

Among obese men (BMI ≥30.0 kg/m²), a greater time spent watching television/videos was associated with a slightly increased risk of prostate cancer. The hazard ratio of 1.28 for 7 or more hours versus less than 1 hour per day was not quite statistically significant, however.

Conversely, among normal-weight men (BMI 18.5–24.9 kg/m²), greater television/video time was associated with a reduced risk of prostate cancer. Again, the hazard ratio of 0.66 for 7 or more versus less than 1 hour per day was not statistically significant.

The hazard ratio among overweight men was 1.04, suggesting no effect on risk. Similar patterns were seen for correlations between total daily sitting time and television/video time and advanced prostate cancer and prostate cancer mortality.

Writing in Cancer Epidemiology, Biomarkers & Prevention, Lynch and co-authors conclude: “Sedentary behavior appears to play a limited role in the development of psotate cancer, however we cannot rule out potential effect modification by body mass index or the impact of measurement error on results.”

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