Sugar consumption is associated with known risk factors for breast cancer. High intake of sweets and foods containing added sugar is associated with increased breast cancer risk. Sugar- and high fructose corn syrup-sweetened soda have also been linked to increased breast cancer risk in several large population studies, although not all are in agreement.
Now a major long-term U.S. prospective study has reported that overweight estrogen receptor positive (ER+) breast cancer survivors with frequent sweetened soda consumption have heightened mortality over time.

Sugar increases breast cancer risk factors

Sugar has been shown to increase markers of oxidative DNA damage in healthy adults. As noted above, sugar consumption is associated with known risk factors for breast cancer, including increased systemic inflammation, higher levels of circulating estradiol (E2), and increased breast density, in addition to obesity and type 2 diabetes. Girls who are frequent consumers of sugar-sweetened beverages are more likely to experience early menarche (first period) at a relatively young age.

Breast cancer has a complex relationship with sugar

Rats fed high-sugar diets were found to develop significantly more mammary tumors than those fed starch-based diets, at both low and high levels of dietary fat, in one study. However, the idea that breast cancer is "fed by sugar" is at best a partial explanation for the association between sugar consumption and breast cancer risk.
All of our cells require energy in the form of glucose to survive. It is true that cancer cells typically consume glucose at a higher rate than normal cells and compounds that cause inhibition of glucose uptake by tumor cells may inhibit their growth and viability. However, cancer cells will obtain glucose from a variety of foods in the diet, not just sugar. Sugar and high fructose corn sugar (a common soda sweetener) also appear to act in direct ways to promote breast cancer, not just as a fuel for cell metabolism and growth.
The rate of glucose uptake by tumor cells is greatly increased under certain circumstances, however. This form of deviant energy metabolism is called the Warburg effect—it appears to be the result of genetic dysregulation in cancer. Cancer cells exhibiting the Warburg effect produce energy mainly through a high level of glycolysis (the breakdown of glucose by enzymes) rather than through a low level of glycolysis as is the case in normal cells. Together with activation of key proliferative and survival signaling pathways, the Warburg effect plays a critical role in tumor development. In this scenario, dietary sugar has the potential to promote tumor growth more directly, although high sugar intake is not necessary for the functioning of Warburg effect.

Latest research links sweetened soda to BC mortality

The long-term prospective study referenced above was designed to investigate the associations between sugar-sweetened soft drink ("soda") consumption and all-cause and breast cancer-specific death in women with invasive breast cancer. The study included breast cancer cases in the Western New York Exposures and Breast Cancer (WEB) Study who were followed for a median of 18.7 years.
The authors used a validated food frequency questionnaire to determine soda consumption. A total of 386 of the 927 women with breast cancer had died by the end of the follow-up period. Consumption of soda ≥ 5 times per week was found to be associated with 1.62 times higher risk of death from any cause and 1.85 times higher risk of breast cancer-specific death compared to never or rarely drinking soda. However, the increased risk of mortality was found among women with (1) ER+, but not ER- breast cancer; and (2) BMI above the median, but not below the median; and for total mortality only, premenopausal, but not postmenopausal, status at diagnosis.
The authors conclude that relatively high intake of sugar-sweetened soda is associated with increased risks of both total and breast cancer-specific mortality among women diagnosed with breast cancer. The results support existing recommendations to limit consumption of sugar-sweetened beverages, including for women with breast cancer, according to the authors.
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