Milk is a complete and rich source of nutrients and has long been regarded as the most cost-effective and nutritious supplement.
However, in recent years, many studies have presented counter-evidence, suggesting that excessive milk consumption is harmful to health. Especially reports that excessive milk intake increases the risk of ovarian cancer in women and prostate cancer in men have caused great confusion among consumers: Is milk carcinogenic or cancer-preventive? To further clarify the relationship between milk and ovarian and prostate cancer, we have reviewed the literature from the past decade, hoping to resolve consumers' doubts through analysis. The analysis results are summarized as follows:
We searched authoritative databases for articles published in the last ten years on the relationship between milk and ovarian and prostate cancer, finding a total of 15 reports. Among them, 8 articles were on the relationship between milk consumption and ovarian cancer (including 1 meta-analysis), and 7 were on the relationship between milk consumption and prostate cancer (including 2 reviews and 1 meta-analysis). Researchers used case-control or cohort studies, combined with dietary survey data, to analyze the relationship between the consumption of milk and dairy products and the risk of ovarian and prostate cancer in the subjects. The number of subjects ranged from a minimum of 86 to a maximum of 80,326. The research focus was on the relationship between the fat, lactose, calcium, and hormonal substances in milk and the incidence of ovarian and prostate cancer.
Some research results suggest that the fat in milk is a saturated fat, and its intake is significantly related to the incidence of prostate cancer; galactose, produced from the breakdown of lactose in the body, is associated with the incidence of ovarian cancer, but only for serous ovarian cancer; the intake of calcium in milk is associated with the risk of prostate cancer in men and ovarian cancer in women. However, the results of the various studies are inconsistent and even contradictory. For example, Daniel et al. found that lactose consumption is not a risk factor for ovarian cancer. Pan et al.'s population-based case-control study in Canada found no association between ovarian cancer and dairy consumption. Case-control studies on risk factors for ovarian cancer conducted by Goodman et al. in the United States and Yen et al. in Taiwan showed that the intake of low-fat milk, calcium, or lactose could reduce the risk of ovarian cancer.
It is worth noting that most of the above-mentioned studies were conducted in developed countries in Europe and America, and their conclusions are highly related to the amount of milk consumed. For example, Berndt studied the relationship between calcium and other nutrient intake and prostate cancer in 454 men aged 46 to 92. The results showed that their average daily calcium intake was 788 mg; within a certain range, an appropriate dose of calcium intake does not cause a significant increase in the risk of prostate cancer. A 13-year follow-up study by Swedish scientist Larsson et al. found that women who consumed dairy products more than 4 times a day had a twice higher incidence of serous ovarian cancer than those who drank milk twice a day. In contrast, the results of the 2002 National Nutrition and Health Survey of Chinese residents showed that the average daily calcium intake of urban and rural residents nationwide was only 391 mg, equivalent to 41% of the recommended intake. Therefore, calcium deficiency is common, especially among children and adolescents in their developmental period, pregnant or lactating women, and the elderly.
In addition, correlation does not equal causation. Even if some studies suggest that excessive intake of certain components in milk is associated with ovarian and prostate cancer, it does not mean that milk itself is carcinogenic. This association has not reached a consistent conclusion across various studies. Moreover, the annual per capita milk consumption in China is only 25.7 kg, far below the 300 kg in European and American countries. Analyzed from a research methodology perspective, many study results have different conditions and poor comparability; moreover, there is a lack of prospective dietary intervention studies. Therefore, it is difficult to draw a convincing scientific conclusion.
Recently, multiple studies abroad have also shown that milk contains various anti-cancer factors such as calcium, vitamins, lactoferrin, and conjugated linoleic acid, and appropriate intake can play a role in anti-cancer and cancer prevention.
Therefore, regarding milk, Chinese consumers need not worry unnecessarily. As long as they can control the amount and maintain a balanced diet, they can maximize the benefits and avoid the harms.