Background The impact of sugar consumption on diabetes and cardiovascular disease risks is well established. In contrast, the level of evidence regarding the role of sugar in cancer onset is still very limited. However, simple sugars could have a deleterious effect on cancer risk via different mechanisms, such as weight gain, but also through inflammation or insulin resistance. We recently showed that an increased consumption of sugary drinks was associated with cancer incidence, in particular, with breast cancer in the NutriNet-Santé cohort (Chazelas BMJ 2019). Objective Our objective was to expand this research to all sugary products and to prospectively investigate the association between the consumption of sugar (simple sugar, added sugar, sugar from different food sources) and risk of breast cancer (overall, premenopausal and postmenopausal) in a large cohort of French adults. Design Population based prospective cohort study. Setting and participants 79,742 female participants aged ≥ 18y (mean age: 41.0±14.0y) from the French NutriNet-Santé cohort (20092019) were included. Consumption of sugar were assessed using repeated 24h-dietary records, designed to register participants’ usual consumption for more than 3,500 different food and beverages items. Main outcome measures Prospective associations between sugar consumption and risk of breast (premenopausal, postmenopausal and both) cancer were assessed by multivariable Cox proportional hazard models adjusted for known risk factors. Results The consumption of sugar was significantly associated with higher breast cancer risk (n=783 cases, HRfor a 10g/d increase=1.05, 95% confidence interval 1.01 to 1.09, P for trend=0.02), so was the consumption of added sugar (n=783 cases, HRfor a 10g/d increase=1.07, 95% confidence interval 1.02 to 1.12, P for trend=0.01) and more specifically with postmenopausal breast cancer (n=459 cases, HRfor a 10g/d increase=1.08, 95% confidence interval 1.01 to 1.16, P for trend=0.02). The consumption of sugar from sugary drinks was significantly associated with breast cancer (n=783 cases, HRfor a 10g/d increase=1.09, 95% confidence interval 1.01 to 1.17, P for trend=0.03). The overall consumption of sugar from sugary food and beverages (excluding fruits) was significantly associated with breast cancer risk (n=783 cases, HRfor a 10g/d increase=1.07, 95% confidence interval 1.02 to 1.11, P for trend=0.003). Conclusion In this large prospective study, a greater consumption of sugar, added sugars, sugary food and beverages was associated with an increased risk of breast cancer, especially after menopause. These results need replication in other large-scale prospective studies. They suggest that sugar and sugary foods, whose consumption is increasing in Western countries, may potentially represent a modifiable risk factor for breast cancer prevention.