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Milk Products and Prostate Cancer

Basic Facts on Prostate Cancer¹

Prostate cancer is the most common cancer among Canadian men: 1 in 8 men will develop prostate cancer during his lifetime (mostly after the age of 60), and 1 in 27 will die from this disease. There is no single cause for prostate cancer, but some factors increase the risk for developing it:

• Age—particularly after 65 (uncommon in men under 50);
• Family history;
• African ancestry.

Some men develop prostate cancer even without any of these risk factors. Recent research has focused on whether diet may contribute to the development of prostate cancer. More research is needed before any definite conclusions can be made about whether certain foods or dietary components play a role in prostate cancer risk.

The Evidence

The 2014 Continuous Update Project report by the World Cancer Research Fund/American Institute for Cancer Research consisted of a systematic review of scientific evidence related to the role of different dietary components and risk for prostate cancer.² The report upheld the conclusion of the 2007 Second Expert Report³ that there is limited evidence for an association between high dairy product consumption and an increased risk of prostate cancer. In addition, the evidence on the association between diets high in calcium and an increased risk of prostate cancer is now considered limited, as compared to the 2007 report, where it was considered to be strong evidence.

In addition, a study based on a nested case-control analysis of a multicentre, randomized, double-blind clinical trial does not support an association between calcium and prostate cancer risk. On the contrary, it suggests that calcium supplementation might reduce the risk. In this study, 672 men from a colorectal adenoma chemoprevention trial were randomly assigned to receive either 3 g of calcium carbonate or a placebo daily for 4 years. After a mean follow-up of 10 years, there were fewer prostate cancer cases in the calcium-treated group. While a non-significant lowered risk for prostate cancer was seen for the calcium-treated group over the entire study period, there was a statistically significant risk reduction during the first 6 years.⁴

This finding is also supported by a prospective study of more than 22,000 healthy Swedish men followed over 30 years, which assessed serum calcium levels and risk of prostate cancer. The hypothesis that a high serum calcium level is a risk factor for prostate cancer was not supported.⁵

Moreover, in a case-control study published in 2012, the association between calcium intake from food and prostate cancer risk was investigated among 533 US veterans. It was found that increased dietary intake of calcium, but not total calcium, was associated with a lower risk for prostate cancer among all races, particularly among black men. Additionally, calcium from food was associated with a lower risk for high-grade prostate cancer among all men.⁶

Potential Mechanisms

Vitamin D
Some studies have found that vitamin D deficiency could be linked to an increased risk of prostate cancer. To date, the potential association between vitamin D and prostate cancer remains unclear.⁷

Calcium
It has been hypothesized that high calcium intake may increase the risk of prostate cancer. However, a causal relationship is not supported between calcium intake and the risk of prostate cancer, whether in the advanced or non-advanced stage, by the totality of evidence from epidemiological studies.⁷

Moreover, according to evidence from a limited number of experimental studies, dietary calcium does not have a role in prostate cancer.⁷

IGF-1 (Insulin-like Growth Factor-1)
IGF-1 is a hormone needed for proper growth and development. IGF-1 is part of a multi-component IGF system, which regulates the proliferation, differentiation and apoptosis of both normal and prostate cancer cells.⁷

The level of IGF-1 is increased by the intake of any type of protein, whether animal or vegetable. In addition, although it has been found that the intake of one serving of milk products daily can increase IGF-1 levels, this was no longer the case after controlling for overall protein intake.⁸

Studies in animals and cell lines have hypothesized that IGF-1 may stimulate the rapid growth of prostate cells and inhibit cell death. However, from experimental and epidemiological data, it appears that high serum levels of IGF-1 may be a tumour marker, rather than an etiological factor for prostate cancer.⁷

Dietary and dairy fat
Early ecological studies have demonstrated that average total fat intake per capita was correlated to prostate cancer mortality. Since then a meta-analysis of prospective cohort studies and more recent large-scale prospective cohort studies have not found an association between dietary fat intake and the risk of prostate cancer.⁷

Phytanic acid is a branched-chain fatty acid found in dairy fat and the fat from ruminant meats. The oxidation of such fatty acids generates hydrogen peroxide, which has been suggested as a potential procarcinogen for prostate cancer. However, the amount of hydrogen peroxide produced through dairy consumption is minute compared to the daily amount produced by the oxidation of exogenous and endogenous lipids or the degradation of amino acids.⁷ There is no evidence that the oxidation of dairy branched-chain fatty acids has an impact on the development of prostate cancer.⁷

Conclusion

The scientific literature to date does not support a conclusive association between milk product consumption or calcium intake and increased risk of prostate cancer.

Keywords: prostate cancer , cancer , calcium