Women who ate more fruit in their adolescent years had a lower risk of breast cancer later on, according to a new study. The research was conducted by Maryam Farvid, a research associate in the department of nutrition at the Harvard T.H. Chan School of Public Health, over the course of two decades.

Attempting to prove causal relationships between food and cancer has always been difficult, and most studies on the matter have been conflicting. However, this is the first to examine the effect of adolescent fruit intake on future cancer development.

For the study, the researchers analyzed 90,476 women aged 27 to 44 who had been involved in the Nurses’ Health Study II. In 1991, all of the women had completed a food and diet questionnaire, and in 1998, about 44,223 of them filled out another questionnaire about their diet during adolescence. From 1991 to 2013, the women were asked about their food and drink consumption every four years, and breast cancer was tracked every two years. Over the course of the two decades, 3,235 women developed breast cancer — 1,347 of whom had completed a questionnaire about their diets in adolescence. The researchers found that more fruit consumption (2.9 servings versus 0.5 servings) during adolescence was linked to a 25 percent lower risk of breast cancer.

Interestingly, it was a greater consumption of apples, bananas, and grapes during adolescence (as well as oranges and kale during early adulthood) that was linked to a lower breast cancer risk. Drinking fruit juice, meanwhile, didn’t appear to have any association.

The study, however, employed self-reporting based on distant memory, and most of us can say that remembering what we ate in teenage years decades later will likely be a foggy and flawed memory. It’s tough to say how accurate the association is. Further studies would be needed, in which researchers track teens throughout their adolescence and measure their fruit intake more closely. Farvid notes that “due to the observational nature of the study, we could not provide evidence of cause and effect.”

“You’ll probably never be able to prove cause and effect, but time and time again the data shows that there’s something to starting out life with a healthy diet,” said Lona Sandon, program director in the department of clinical nutrition at the UT Southwestern Medical Center at Dallas. “Fruit has vitamins, minerals, and all sorts of plant compounds that appear to be healthy for us. And it’s also worth noting that if teens are consuming more fruit, what are they not consuming instead? Are they eating less candy, cookies, cakes, and soda? That may play a role as well.”

The current study doesn’t prove a direct link between consuming fruit and lowered breast cancer risk, and most other studies on this subject have been inconsistent. But according to the Cancer Research UK, things like diet and lifestyle are still generally believed to prevent some cancer cases. They note that four in 10 UK cancer cases can be prevented, mainly by avoiding tobacco and smoking, overconsumption of alcohol, UV exposure, air pollution, infections and HPV, and workplace toxins. On top of that, maintaining a healthy lifestyle through proper nutrition and physical activity can help prevent some cancer, the organization notes.

Source: Farvid M, Chen W, Michels K, Cho E, Willett W, Eliassen A. Fruit and vegetable consumption in adolescence and early adulthood and risk of breast cancer: population based cohort study. The BMJ. 2016.