Breast cancer has now surpassed lung cancer as the world’s most often diagnosed cancer, and which leading cause of cancer-related deaths for women in many countries. While genetics can really increase the risk of the disease, for most women lifestyle factors, such as alcohol or obesity or obesity, is a major influence on the development of breast cancer. Now, two separate studies, both published in 2020, have identified cow’s milk as another possible risk factor for breast cancer.
The first study, which looked at 33,780 Swedish women since 1997, found that about 300 ml of cow’s milk per day (equivalent to a large mug) increased the risk of breast cancer by about a third compared to women who did not drink milk.
The second study, from the United States, looked at 52,795 over a period of almost eight years and found that women who drank about 300 milliliters of milk per day had a 50% increased risk of breast cancer compared to those who drank very little milk.
Both studies showed that the risk was mostly limited to postmenopausal women who developed a type of estrogen-stimulated breast cancer, called estrogen receptor positive breast cancer. There was no increased risk of other types of breast cancer that are dependent on other growth factors (e.g. HER2-positive breast cancer).
However, due to their design, the studies could only conclude that there was a link between milk consumption and breast cancer – they could not prove that drinking milk caused cancer. The authors of the studies took into account other known causes of breast cancer that may have explained their results, such as the woman’s age when she had her first period and menopause and alcohol consumption. But the authors still could not completely discount all other possible explanations for their results. So how important is milk as a cause of this type of breast cancer?
To understand why cow’s milk may increase the risk of estrogen receptor positive breast cancer, it is important to look at biological studies that can help us see what mechanisms take place in the body. Cow’s milk contains natural stimulants for cell growth and division. These stimuli work in the body by raising the levels of a growth factor called IGF1 (insulin-like growth factor 1). Studies show that in humans, it is these elevated levels of IGF1 that are strongly involved to increase the risk of breast cancer, which may be the reason why drinking milk is linked at greater risk.
Interestingly, fermenting dairy products (yogurt and cheese) did not increase the risk of breast cancer in any of the previous studies. This may be due to yogurt and cheese not increase IGF1 levels in the body. This may be because the IGF1-stimulating factors found in milk are lost during the production of cheese and yogurt.
IGF1 does not increase the risk of breast cancer on its own. Rather, it is its ability to stimulate cell growth greatly enlarged of estrogen. This may explain why in the two studies, high milk consumption increased the risk of estrogen receptor-positive breast cancer, but not for other types. It may be that both estrogen and IGF1 are needed for breast cells to become cancerous – and that this can only happen in cells that respond to estrogen as well as IGF1.
Other risk factors
In addition to milk, many other factors that increase the risk of breast cancer also work by increasing the levels of IGF1 or estrogen in the body. Obesity raises levels for both IGF1 and estrogen in postmenopausal women. And an early menarche, a late menopause and drinking alcohol everyone is increasing the duration and amount of estrogen exposure of the breast cells.
Because many risk factors affect estrogen and IGF1 levels, it is too simplistic to point to the blame for breast cancer on only one food, such as milk. Many factors need to be considered. This may help explain why, for example, Belgium, the Netherlands and Luxembourg occupy top three places in the world for the incidence of breast cancer. Milk consumption is high in the Netherlands, but not very high in Belgium or Luxembourg. And while obesity For women in these countries are tall, they are certainly not the tallest in the world. Neither is theirs alcohol consumption especially loud. So it is probably the merging of many risk factors that raise estrogen and IGF1 levels that contributes to the particularly high incidence of breast cancer in the Benelux countries.
It is equally important to consider protective factors. Physical activity lowers the risk of breast cancer and improves survival in patients with breast cancer, and this is linked to lower IGF1 levels. Diet can also protect against increased levels of estrogen and IGF1. Some foods contain substances called phytoestrogens that block the effect of estrogen. For example, extra virgin olive oil is one exceptionally rich source. This may also partly explain why women who eat a Mediterranean diet (which traditionally do not contain cow’s milk) are on a lower risk of breast cancer. So while cow’s milk may be a risk factor for breast cancer, it works in conjunction with many other risk factors.
Author: Richard Hoffman – Assistant Professor, Nutritional Biochemistry, University of Hertfordshire
Source: sn.dk