Re: Insulin Resistance and Prostate Cancer Risk

Extract

In three papers from the same case–control series recruited from Shanghai, China, Hsing et al. (1–3) have reported statistically significant associations between prostate cancer risk and aspects of insulin resistance syndrome. First, they observed an increase in prostate cancer risk associated with abdominal obesity, measured by waist-to-hip ratio (odds ratio [OR] = 2.71 for highest versus lowest quartile) (1). Subsequently, they reported an OR of 2.80 for highest versus lowest tertile of insulin (2), and they reported an OR of 2.78 for highest versus lowest tertile of an index of insulin resistance, calculated from fasting insulin and blood glucose levels in a homeostasis model (HOMA IR) (3). Equivalent results, but in the opposite direction, were found for an index of insulin sensitivity, instead of insulin resistance, calculated as “QUICKI.” Hsing et al. pointed out the need for prospective studies on insulin resistance syndrome and prostate cancer risk.

Prompted by the work of Hsing et al. (1–3), we re-analyzed our data from The Northern Sweden Health and Disease Cohort, in which prostate cancer risk was not associated with body mass index (BMI) or insulin in blood samples collected, on average, 4 years before cancer diagnosis (4). We then calculated the ORs for indices of insulin resistance (HOMA IR) and insulin sensitivity (QUICKI), and we found no association between these indices or insulin levels and prostate cancer risk (Table 1). Given the strong correlation between insulin and HOMA IR (Spearman coefficient of correlation, r = .95) and between insulin and QUICKI (r = −.95) in our study, it is not surprising that all three measures resulted in very similar risk estimates.