It is difficult to draw firm conclusions about how to eat and drink to avoid breast cancer. Dietary studies often rely on self-reporting, and dietary habits change over a lifetime - both of which are difficult for researchers. But one link is well established: even moderate alcohol consumption increases the risk of getting the disease, says professor Alicja Wolk.
Text: Annika Lund, first published in Medicinsk Vetenskap nr 1 2024 / Spotlight on breast cancer.
What is known about diet and breast cancer?
"With the strongest evidence we know that alcohol increases the risk of breast cancer, even at moderate intake. Ten grams of alcohol per day increases the risk by nine percent. This is equivalent to about one deciliter of wine a (per?) day or just under a bottle of wine a (per?) week - or half a bottle at two dinners a (per?) week. However, this is all calculated at group level, so for an individual woman the risk may be lower or higher".
Is there anything that is protective?
"According to the current state of knowledge, based on studies published so far, calcium, found in dairy products, and so-called carotenoids have a protective effect, but the evidence is weaker than for alcohol. Carotenoids are found in many vegetables, such as carrots, spinach, tomatoes, peppers and broccoli, but also in egg yolks".
What to avoid?
"Apart from alcohol, I would say dietary supplements. For most people, supplements are just unnecessary and expensive, but for those who take them in large quantities, they can be harmful. If you have a nutritional deficiency, as diagnosed by a doctor, you may need supplements. However, a varied diet provides sufficient quantities of these substances and excesses can be harmful. In addition, we know that red meat and processed meat increase the risk of bowel cancer in particular, but the link with breast cancer is uncertain".
But sugar and other controversial items - what can we say about them?
"For many foods, the state of knowledge is unclear. A lot of sugar is not good, partly because it can lead to obesity, which is not good for breast cancer. Phytoestrogens, which are converted to oestrogen-like substances in the body, are also an unclear area. Phytoestrogens are found in beans, for example, and therefore also in soy and tofu. Here, different studies have given results difficult to interpret".
So all in all, how should you eat?
"Don't just think about breast cancer, eat with your overall health in mind. The National Food Agency's recommendations are good".
How are you doing research in this topic?
"We are following a group of 60 000 women since the 1980s, invited via mammography screening. They have answered questionnaires about their diet on several occasions. We are part of an international collaboration led by the Harvard School of Public Health and share our original data with about 30 other research groups. This allows for larger study populations and therefore more reliable results".
Alicja Wolk is professor at the Institute of Environmental Medicine.
