New research has found that women who gain weight in early adulthood are at a decreased risk of breast cancer before menopause.

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New research suggests that weight gain may have a protective effect against breast cancer before menopause.

A new study, which features in the International Journal of Cancer, has found that women who gain weight from early adulthood are at a reduced risk of developing breast cancer before they reach menopause.

The study builds on previous research, which found that women who weighed more as young adults had a reduced risk of premenopausal breast cancer.

The World Health Organization (WHO) note that breast cancer is the most common cancer in women, among whom it accounts for the highest number of cancer-related deaths.

According to statistics that the Centers for Disease Control and Prevention (CDC) and the National Cancer Institute compiled, 41,487 women died of breast cancer in the United States in 2016, the latest year for which there are records.

The present study explored the previous findings in more detail, aiming to discover whether gaining weight from early adulthood (aged 18–24 years) up to the age of between 40 and the early 50s also affected a woman’s risk of developing breast cancer before menopause.

Previously this had been difficult to determine because of the relatively low rates of breast cancer in younger women.

The study looked at data from 628,463 women from many separate studies around the world. It divided these women into six age groups, gathered information on their weight at a minimum of two different ages, and followed them for an average of 10.1 years.

The study analyzed a significant amount of additional information about the women to account for possible confounding factors and to enable the authors to understand, as far as possible, the effects of weight gain separately to any other factors.

Of the 628,463 women in the study, 10,886 went on to develop breast cancer before menopause.

By comparing these data against the amount of weight that the women gained, the researchers found that gaining 10 kilograms (kg) or more of weight from early adulthood resulted in a lower risk of developing breast cancer before menopause.

Weight gain between the age ranges of 18–24 years and 45–54 years reduced the risk of breast cancer by 4% for every 5 kg.

In contrast, gaining weight after the age of 35–44 years had no effect on the chances of a woman developing breast cancer before menopause. This finding may suggest that cumulative exposure to excess weight is the key factor associated with breast cancer risk.

However, more research is necessary to know this for sure, as well as to determine what precise mechanism accounts for the relationship between greater weight gain and lower breast cancer risk.

According to Dr. Minouk Schoemaker, a senior staff scientist in cancer epidemiology at The Institute of Cancer Research, London, and lead author of the study:

“The link between a higher body mass index and a lower breast cancer risk before menopause has puzzled researchers for a while now. In our large-scale international study, we were able to tease out the effects in more detail than ever before.”

“We found that while higher weight in early adulthood was most strongly linked to reducing breast cancer risk, later weight gain had an independent effect in bringing risk down further.”

“But we know that the protective effect of a higher weight is reversed after menopause, when being heavier increases women’s breast cancer risk.”

“Women shouldn’t consider gaining weight as a way to prevent breast cancer — but understanding the biological reasons behind the link between weight and breast cancer risk could, in future, lead to new ways to prevent the disease.”

– Dr. Minouk Schoemaker

The present study received funding from a much wider landmark study called the Breast Cancer Now Generations Study, which researchers set up in 2004 to determine the causes of breast cancer. It is following 113,000 women in the United Kingdom over a period of 40 years.

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