Dairy intake and prostate cancer survival.

Abstract

I have recently read with interest the article entitled “Dairy intake in relation to prostate cancer survival.” by Downer et al.1 that examined the effect of dairy nutrient intake on prostate cancer progression in 525 patients with high dairy consumption. The authors confirmed 222 deaths with prostate cancer-specific and 268 deaths by other causes. Adjusted hazard ratio (HR) (95% confidence interval (CI)) of high-fat milk intake for prostate cancer-specific death in 230 patients with localized stage at diagnosis was 4.86 (1.52–15.57). However, the significance of adjusted HR disappeared, when vitamin D was included for the adjustment. In contrast, adjusted HR (95% CI) of low-fat milk intake for prostate cancer-specific death in 295 patients with advanced stage at diagnosis was 1.93 (1.06–3.50) when vitamin D was included for the adjustment. Furthermore, HR (95% CI) of relatively higher amount of high-fat milk versus low-fat milk intake for prostate cancer-specific death in 230 patients with localized stage at diagnosis was 3.28 (1.16–9.30). I have some concerns about their study. First, the authors presented some speculations about the mechanism of the effect of high-fat milk intake on promoting prostate cancer progression, although there is a difficulty of confirming it. I understand that the risk of dairy intake on incident prostate cancer and prostate cancer mortality after incidence should be separated. About incident studies, Aune et al.2 conducted a meta-analysis of prospective studies on intakes of dairy products and calcium for prostate cancer risk. Pooled HRs (95% CIs) of intakes of total dairy products, total milk, low-fat milk, cheese and dietary calcium for prostate cancer risk were 1.07 (1.02–1.12), 1.03 (1.00–1.07), 1.06 (1.01–1.11), 1.09 (1.02–1.18) and 1.05 (1.02–1.09), respectively. By considering the positive association between intakes of dairy products and incident prostate cancer by a meta-analysis, I strongly recommend a meta-analysis on the causal association between dairy intake and prostate cancer survival as a further study. Second, I have a query on the censored cases of 268 deaths by other causes of prostate cancer. The significance of HR changes by different models of adjustment and wide range of 95% CI on significant HR was observed. Taken together, stable estimates of HR with a sufficient number of events are needed to confirm the association. Finally, health promotion act on nutrients in patients with prostate cancer should be considered. Although there had been inconsistent results by meta-analysis on the association between intakes of dairy products and prostate cancer risk.3, 4 Aune et al.2 updated the relationship. Nevertheless, established recommendation for the intakes of dairy products in patients with different stages of prostate cancer has not confirmed yet. Anyway, further studies are needed to confirm the causal association. The author declares no conflict of interest.