Rumor:

A new study was published in the "International Journal of Epidemiology" that drinking milk may cause breast cancer.

Popular science interpretation:

Almost every once in a while, there is a controversy about whether drinking milk is good or bad for health. A recent worrying news is that the International Journal of Epidemiology published a latest study that drinking milk may cause breast cancer [1]!

In this study, American researchers used a food frequency questionnaire to assess the dietary intake of 52,795 North American women (average age at enrollment: 57.1 years old, without cancer at the time) and followed them for 7.9 years. There were 1,057 new cases of breast cancer during this period. Researchers analyzed the data and found a significant association between milk and breast cancer risk, with higher milk intake increasing the risk. And there was no significant difference in the risk of breast cancer between whole milk and low-fat milk.

Now, the anti-milk fighters have come forward again and have long said that milk cannot be drunk! Cow's milk is for cows to drink!

Don’t rush to conclusions, let’s analyze the relevant research.

1. The age of the study subjects is limited, which may affect the research results

This study was conducted among more than 50,000 middle-aged and elderly women in the United States. The age of 52.7 is already the age of menopause. , it does not mean that people of other ages will have the same results. For example, a similar survey conducted among young women aged 27 to 44 reached inconsistent conclusions [2].

In 1991, researchers selected 90,503 women of childbearing age between the ages of 27 and 44, and also used a food frequency questionnaire to investigate dairy product consumption. From 1991 to 2013, 3191 cases of breast cancer were discovered. In 1998, 44,264 women recalled adolescent dairy consumption. This subgroup of women was followed from 1998 to 2013, and 1,318 cases of breast cancer were discovered.

This study's data analysis shows that eating dairy products, including milk, during adolescence or early adulthood, that is, when you are young, does not increase the risk of breast cancer.

From this point of view, the study mentioned at the beginning of the article should at least conclude that "drinking milk by middle-aged and elderly women may increase the risk of breast cancer" and cannot be extended to "children, teenagers, and young women who drink milk may increase the risk of breast cancer." Promote breast cancer".

2. There is no consistent conclusion on the relationship between milk and cancer

In the 2010 World Cancer Research Fund (WCRF) report on breast cancer, dairy intake and breast cancer The evidence for cancer risk is inconclusive [3].

Although some studies suggest that dairy intake increases the risk of breast cancer, some meta-analyses suggest that dairy products are not associated with breast cancer and may even reduce the incidence of breast cancer.

A study collected prospective cohort studies on dairy intake and breast cancer risk from the PubMed database in January 2011, and included 18 eligible studies involving 24,187 cases and 1,063,471 individuals. participants. The analysis found that increased dairy intake, but not milk intake, may be associated with a lower risk of breast cancer. The association with reduced breast cancer risk was stronger for low-fat dairy products than for high-fat dairy products, and stronger in premenopausal women than in postmenopausal women (this also seems to confirm the issue we mentioned earlier about the study population).

Another study found that high dairy intake (gt; 600 g per day) and moderate dairy intake (gt; 600 g per day) compared with low dairy intake of less than 400 g per day 400 to 600 grams) was associated with a modest reduction in the risk of breast cancer (reductions of 10 and 6, respectively).

An analysis of different types of dairy products found that intake of yogurt and low-fat dairy products was inversely related to the risk of breast cancer, while other types of dairy products did not reduce risk.

In addition, analysis of differences across ethnic groups found that among Asians, the highest dairy intake was associated with a reduced risk of breast cancer.

In other words, for Asians, eating dairy products not only does not cause breast cancer, but may also reduce the risk of breast cancer, especially yogurt and low-fat milk.

Why are the results so different? On the one hand, there may be differences in the respondent populations, ages, eating habits, and analysis methods in each study. On the other hand, the sources and varieties of dairy products may also be different.

Dairy products contain a variety of biologically active compounds, some of which have positive effects on cancer prevention, while others have negative effects. The positive effects may be related to calcium, lactoferrin, butyric acid, conjugated linoleic acid and lactic acid bacteria fermentation products in dairy products, while the negative effects may be related to casein and insulin-like growth factor I (IGF-1). content related.

The use of growth hormone in dairy cows, commonly used in U.S. milk production, increases IGF-1 levels. This ingredient is thought to increase the risk of breast cancer. Therefore, many experts in the United States prefer organic milk that does not require hormone treatment. However, neither my country nor Australia (an important producer of imported dairy products in China) use growth hormone to treat dairy cows, so the risk of this factor is relatively lower.

There are many dietary factors related to breast cancer, and other dietary habits besides dairy products also have an impact. For example, epidemiological studies have shown that higher intakes of cruciferous vegetables, dark green leafy vegetables, legumes, and whole grains are beneficial to the prevention of breast cancer. Processed meat products, sweet drinks and other foods may promote breast cancer.

Therefore, the problem of breast cancer cannot only consider dairy products as a factor.

3. There is no need to give up dairy products

No country currently calls on its citizens to completely give up dairy products, including European and American countries that are wary of dairy products. As far as the current dietary situation of Chinese residents is concerned, milk is still of great significance:

Milk is a high-quality source of protein. 100 grams of milk contains 3% of high-quality protein. At the same time, milk is easy to drink and portable. It is suitable for consumption with a variety of foods. It is a good source of high-quality protein that can be supplemented at any time.

Milk is rich in B vitamins and is also a source of vitamin A, vitamin D, and zinc. Drinking 300 grams of milk can achieve 10 to 32 of the recommended intake.

Milk is an important source of the mineral calcium, containing over 100 mg of calcium per 100 g of milk. If you drink 300 grams of milk every day, you can supply more than one-third of the daily calcium nutritional goal.

For ordinary Chinese, if they only consume no more than 300 grams of dairy products per day, they will have relatively few negative effects on the premise of effectively increasing the supply of nutrients.

According to current research, dairy intake can reduce body fat, help prevent childhood obesity, and reduce the risk of type 2 diabetes, stroke, and colon cancer.

The Chinese Nutrition Society organized an expert group to collect relevant research on dairy products and analyzed the evidence on the relationship between dairy products and health [7]. Meta-analyses indicate that low-fat milk intake is associated with a lower risk of breast cancer, while whole-fat milk intake is not associated with breast cancer risk (evidence level B).

(Popular science: The evidence of evidence-based medicine is graded from A to D***4. Level A is the highest, which is the conclusion of level I clinical research with consistent results. Level B is the conclusion of level II, Conclusions of Level III clinical studies or inferences from Level I clinical studies)

A multinational epidemiological survey [8] published in The Lancet in 2018 found that compared with not consuming dairy products. A serving of milk or yogurt (about 1 cup) per day can help reduce the risk of cardiovascular and cerebrovascular diseases.

From a health perspective, fermented dairy products are the safest among various dairy products. Lactic acid fermentation can effectively reduce IGF-1 and reduce concerns about its increased risk of cancer. Yogurt, in particular, has plenty of evidence to help prevent obesity, diabetes and cardiovascular disease, and no negative research results have been found so far.

4. How should we drink milk?

First of all, it is safer to choose fermented milk.

Yogurt and cheese are both examples of fermented milk. However, the yogurt on the market now contains more and more added sugar for a better taste, and the intake of refined sugar is harmful to health. Therefore, pay attention to buying low-sugar or sugar-free yogurt, and at least buy yogurt with a carbohydrate content of less than 12 per 100 grams.

Secondly, control the amount of milk you drink. For more than 30 years, the Chinese nutrition community has insisted on recommending that each person consume 300 grams of milk or an equivalent amount of dairy products per day. Compared with other countries, this number is not high and is very safe. For example, Australia’s recommended amount is 750 ml, the United States is 720 ml, India is 300 ml, and Japan’s recommended amount is 200~300 ml. Only South Africa (250 ml) and South Korea (200 g) are lower than my country’s recommended amount [9 ].

So, there is no need to be afraid of dairy foods just because of the results of one study. If you still have concerns about drinking milk, you can substitute yogurt with less added sugar.

References:

1 Fraser GE, Jaceldo-Siegl K, Orlich M, et al. Dairy, soy, and risk of breast cancer: those confounded milks. Int J Epidemiol. 2020 Feb 25.

2 Maryam S, Farvid A. Eliassen H, et al. Dairy consumption in adolescence and early adulthood and risk of breast cancer Cancer Epidemiol Biomarkers Prev. 2018 May; 27(5): 575584 .

3.World Cancer Research Fund/American Institute for Cancer Research. Food, nutrition, physical activity, and the prevention of breast cancer. London, UK: WCRF International; 2010.

4.Dong JY, Zhang L, He K, Qin LQ. Dairy consumption and risk of breast cancer: a meta-analysis of prospective cohort studies. Breast Cancer Res Treat. 2011; 127(1): 2331.

5.Zang J, Shen M, Du S, Chen T, Zou S. The association between dairy intake and breast cancer in western and Asian populations: a systematic review and meta-analysis.J Breast Cancer. 2015; 18( 4): 31322.

6 Thorning TK, Raben A, Tholstrup T, et al. Milk and dairy products: good or bad for human health? An assessment of the totality of scientific evidence. Food Nutr Res. 2016, 60: 32527

7 Compiled by Chinese Nutrition Society. Food and Health: Knowledge of Scientific Evidence. People's Medical Publishing House, 2016

8 Dehghan M, Mente A, Rangarajan S, et al. Association of dairy intake with cardiovascular disease and mortality in 21 countries from five continents (PURE): a prospective cohort study. Lancet. September 11, 2018 http://dx.doi.org/10.1016/S0140-6736 (

18)31812-9

9 Yang Yuexin, it is imperative to advocate milk consumption. China Dairy Industry. 2017, 183(3): 2-5

Rumor-refuting expert:

Wu Jia, registered nutritionist

Fan Zhihong, director of the Chinese Nutrition Society, associate professor, School of Food, China Agricultural University