Breast cancer rates are rising worldwide. These habit shifts could lower your risk.

Despite enormous progress in treatments, breast cancer remains the most common cancer among women worldwide, a new study found. And the trend shows no signs of slowing down: Global cases are expected to increase from 2.3 million in 2023 to 3.5 million by 2050, according to research by the University of Washington Institute for Health Metrics and Evaluation (IHME), published Monday.

What’s more, the steepest increase in new breast cancer diagnoses in the U.S. is among women under 50. While age and genetics are still strong predictors of who will develop the disease, the new research found that lifestyle factors — including smoking, eating red meat, spending too much time sitting, and carrying excess weight — are responsible for a quarter of the healthy years of life lost to breast cancer. Here’s what to know.

A tale of two trends

Breast cancer affects countries in different ways. There are many more cases of breast cancer diagnosed in high-income countries — including the U.S., U.K. and Canada — where robust health care systems provide better access to screening, compared to low-income countries, including those in sub-Saharan Africa. Breast cancer rates are also rising far more sharply in low-income countries, increasing by 147% between 1990 and 2023, compared to high-income countries, which saw only a 1.2% increase in 2023.

The gap is even wider when it comes to breast cancer deaths. Since 1990, mortality rates have fallen by 30% in wealthy nations, while doubling in poorer countries. But the U.S. and its peers are not immune from the rising rates of breast cancer: New cases in the U.S. have been increasing by about 1% per year since around 2012, with a sharper 1.4% increase among women under 50.

Why is this happening?

When it comes to the steady rise in breast cancer cases, “there are a lot of things happening at once,” Dr. Jennifer Keating Litton, an MD Anderson breast cancer oncologist, tells Yahoo. “Incidence is increasing, but we are also seeing that people are living longer and a higher percentage of people are cured.”

Experts have yet to pinpoint exactly why rates are rising in the U.S. and elsewhere, but one thing is clear, says Litton: It’s not just the result of more people getting screened; the rise in breast cancer cases is real. “There are a lot of different factors for why any one individual gets breast cancer … but we do see trends in increases in weight and alcohol” — all of which are risk factors for breast cancer, Litton says.

Age, genetics and pregnancy all play a role

Genetics — particularly BRCA mutations — and family history can play a major role in breast cancer risk. But most people who develop the disease do not have an inherited risk. Aside from being born female, age is the most significant risk factor for breast cancer, with most cases diagnosed in those over 50. Yet, in the U.S., rates are rising faster in women under 50 than in those older women. More than two-thirds of cancers diagnosed under age 50 occur in women, and breast cancer is the most common type. This has led many experts to point the finger at a well-known breast cancer risk factor: A woman’s age when she has her first child.

Full-term pregnancy and breastfeeding cause lasting changes to a woman’s breast tissue that reduce the risk that cells will mutate and become cancerous. In the U.S. and many other wealthy nations, more women are waiting longer to have children, or not having them at all, extending the time when those mutations can occur. That’s likely contributing to rising breast cancer incidence, especially among younger women, but it isn’t the whole story, Mary Beth Terry, a professor of epidemiology and environmental sciences at Columbia University and Silent Spring Institute, specializing in breast cancer, tells Yahoo.

“People will say first off that if [breast cancer rates] are going up, it’s because fertility rates are declining,” she says. But Terry and her colleagues have studied the rising global incidence of breast cancer and “we have not found that you can explain these trends by looking at fertility patterns,” she explains. In fact, her research found similar breast cancer increases even in countries where fertility rates are still very high. “It’s important to know that [delaying] pregnancy is not a carcinogen,” Terry says.

So what else is at play? It’s complicated.

Diet, obesity and sedentary lifestyles influence breast cancer risk

Lifestyle and environmental factors play a big role in breast cancer risk and may be driving the continued rise in cases of the disease. They also strongly influence how long someone lives — and how healthy those years are — after a breast cancer diagnosis.

The researchers behind the new IHME study calculated how much each of several lifestyle factors contributed to the number of healthy years of life lost to breast cancer. The top contributing factor was diet, accounting for about 10.8% of years women worldwide spent ill due to breast cancer. Having a diet high in red meat is an especially powerful risk factor, the study found.

That’s because red meat contains fat, which can help fuel the growth of cancer cells. But perhaps more important, it’s often cooked at high temperatures. Barbecuing and other high-temperature cooking methods produce carcinogens that are specifically associated with breast cancer, says Terry.

Chronic inflammation, inflammatory diets (including those high in ultra-processed foods) and obesity can raise the risk of cancer — including breast cancer — because inflammation itself can damage cells, increasing the risks that they become cancerous.

What you can do to reduce your risk

You can’t change your genetics, but you can change your habits. “I think that we should all be doing things to try to improve our healthy lifestyle,” says Litton. “That [means] healthier eating, regular exercise, and the number one across the board is no smoking. That in and of itself would significantly reduce the risk of [many] cancers.”

Cutting back on red meat and other foods cooked at high temperatures can also have a meaningful impact on breast cancer risk, specifically, says Terry. And adopting an anti-inflammatory diet, such as the Mediterranean diet, may help reduce the risk of cancer, including breast cancer, along with other chronic diseases.

While a sedentary lifestyle accounts for just 2% of healthy years lost to breast cancer worldwide, according to the new study, Terry says that two of the clearest ways to cut breast cancer risk (and virtually every chronic disease) are simple: move more and drink less. Both can also help women have better outcomes if they’re diagnosed with breast cancer.

Taking action to reduce your breast cancer risk not only protects your health — it can also benefit future children and even your grandchildren. “Breast cancer incidence is influenced not just by your own exposures throughout your life, but also your mother’s and your grandmother’s,” Terry explains. So taking steps toward a healthier lifestyle could help future generations too.