A government-funded long term study of 76,628 women found that normal weight and overweight women (BMI under 30) who smoked were at a higher risk of breast cancer compared to no added risk in obese women (BMI over 30). The longer normal weight and overweight women smoked, the higher the risk. These results surprised researchers because estrogen fuels a lot of breast cancers and fat tissue produces it. They think the risk of breast cancer from obesity is masking the smaller risk from smoking and also hypothesize the obese women die of other problems such as heart disease before cancer even develops. Researchers want to emphasize more studies need to be done before they can confirm or refute the possible relationship between smoking, weight and the risk of breast cancer.