A Swedish research team examined data from more than 35,000 middle aged and older women, tracked over a decade, and discovered a link between multivitamin use and a higher risk of breast cancer. Their findings, published in the American Journal of Clinical Nutrition, raised concerns about public health, prompting the need for further investigation.
Many women turn to multivitamins hoping for protection against chronic diseases like cancer and heart disease. Yet, a significant US study in 2009, involving over 160,000 postmenopausal women, found no solid evidence supporting the notion that long-term multivitamin use altered their risk of common cancers, cardiovascular disease, or premature death.
However, the impact of multivitamins specifically on breast cancer remained uncertain, as pointed out by the Swedish researchers. Lead author Dr. Susanna C. Larsson and her team, from the Karolinska Institutet, analyzed data from the Swedish Mammography Cohort comprising 35,329 cancer-free women aged 49 to 83 in 1997, focusing on their multivitamin usage and breast cancer risk factors.
Their findings showed that out of 974 women diagnosed with incident breast cancer over a mean follow up of 9.5 years, 293 belonged to the 9,017 women who reported using multivitamins. Use of multivitamins was linked to a statistically significant 19% increased risk of breast cancer. After adjusting for various lifestyle factors like weight, diet, smoking, exercise, and family history of breast cancer, the relative risk of women who reported using multivitamins was 1.19, with confidence interval ranging from 1.04 to 1.37.
The authors said that their observations merely suggested an association, not a causation, between multivitamin use and breast cancer risk. There could be something they did not measure that influenced this link, Larsson pointed out, emphasizing the relatively minor impact of multivitamins on an individual's breast cancer risk.
Nonetheless, considering the widespread use of multivitamins, the study holds an important public health message.
Speculating on what the biological reasons might be, the researchers mentioned various previous studies that taken as a whole reveal a conflicting picture. For instance, some studies on folic acid suggested it increases breast cancer risk while others suggested it has no effect and may even decrease it.
While the biological mechanisms behind this link remain unclear, Larsson advised opting for a diverse and healthy diet over relying solely on pills for essential nutrients.