Milk Products and Prostate Cancer

Basic facts on prostate cancer

According to the Canadian Cancer Society, prostate cancer is the most common cancer in Canadian men.¹ The risk increases as men get older and it is most often diagnosed in men in their 60s. While there is no known cause, a number of other factors are known to increase the risk of prostate cancer. These include a family history of prostate cancer, black ethnicity (including African or Caribbean ancestry) and being overweight.

The evidence

The 2020 IARC World Cancer Report published by the WHO International Agency for Research on Cancer indicates that there is limited evidence of an association between diet, nutrition, and lifestyle factors, including dairy products or dietary calcium, and prostate cancer.²

The IARC report notes the lack of consistent evidence relating to dietary and lifestyle factors makes it difficult to identify modifiable risk factors for the prevention of prostate cancer. In men diagnosed with prostate cancer, risk factors related to obesity appear to be associated with unfavourable outcomes.

According to the Third Expert Report published in 2018 by the World Cancer Research Fund International and the American Institute for Cancer Research, there is no strong evidence that dairy products or diets high in calcium increase the risk of prostate cancer.³  The 2018 report³ upheld the conclusion of the 2007 Second Expert Report⁴ that for a higher consumption of dairy products, the evidence suggesting an increased risk is limited. In addition, the evidence on the association between diets high in calcium and an increased risk of prostate cancer was downgraded to “limited suggestive”, as compared to the 2007 report, where it was considered to be strong evidence.

Potential mechanisms

Vitamin D
Although some studies have suggested that vitamin D deficiency could be linked to an increased risk of prostate cancer,⁵ the 2020 IARC World Cancer Report notes there is no consistent evidence of an association between vitamin D and prostate cancer risk.²

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 (cell death) of both normal and prostate cancer cells.⁵

The level of IGF-1 is increased by the intake of any type of protein, whether animal or vegetable. Although it has been found that the intake of one serving of milk products daily can increase IGF-1 levels, this association did not persist after controlling for overall protein intake.⁶

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.⁵

Additionally, evidence suggests differential associations of milk and the IGF pathway with prostate cancer risk.⁷ Milk intake is associated with higher levels of both IGF-1 and IGFBP-3 (Insulin-like Growth Factor Binding Protein-3). While IGF-1 may be associated with an increased risk, IGFBP-3 appears to be associated with a reduced risk of prostate cancer.⁷   

Dietary fat

A 2015 systematic review and dose-response meta-analysis by Xu et al. concluded that fat is not associated with prostate cancer.⁸ This meta-analysis consisting of 14 cohort studies, with a total of over 750,000 participants and 37,349 cases, found no evidence of an association between total fat, saturated, polyunsaturated, or monounsaturated fat intake and prostate cancer or advanced stage prostate cancer risk.  

Conclusion 

The totality of the scientific evidence to date does not support a clear association between dairy product consumption or calcium intake and increased risk of prostate cancer. The evidence is qualified as suggestive and limited.