But when researchers looked at specific types of cancer, they found that both men and women with the highest blood sugar levels were more likely to have pancreatic cancer, urinary tract cancer, and malignant melanoma (the most deadly type of skin cancer) than those with the lowest blood sugar levels.
Keeping blood sugar levels within the normal range "may reduce cancer risk," write the researchers, who included Par Stattin, MD, PhD, of Sweden's Umea University Hospital.
For the study, Stattin's team invited all residents of a county in northern Sweden to sign up for the study when they were 40, 50, or 60 years old.
Most participants had normal results in both tests. The data show normal blood sugar results for at least 85% of the group after fasting and at least 92% after the sugary drink.
The researchers followed participants for eight years, on average.
Overall, women with the highest blood sugar levels upon joining the study were more likely to be diagnosed with cancer before its end, compared with women with the lowest blood sugar levels.
Also, cancer of the lining of the uterus (endometrial cancer) was more common in women with the highest blood sugar levels, compared with those with the lowest blood sugar levels.
Breast cancer was more common for women younger than 49 with high blood sugar levels, compared with those with the lowest blood sugar levels, the study also shows.
The results held when researchers considered other factors, such as participants' weight and age.
Their study appears in the March edition of Diabetes Care.
The study doesn't prove that high blood sugar levels cause cancer or that normal blood sugar levels prevent it.
Doctors often can't explain exactly why one person develops cancer and another doesn't. A complex mix of genetic and lifestyle factors may affect cancer risk.
Also, the study didn't track all possible cancer influences. For instance, researchers didn't know the participants' diet, exercise habits, or family history of cancer.
They also didn't check participants' blood sugar over time.
More research is needed, but meanwhile, there's no reason not to get blood sugar under control.
Doing so may help prevent diabetes and heart disease, besides possibly making cancer less likely, Stattin's team notes.
Don't know your blood sugar level? Your doctor can run a quick blood test and -- if necessary -- provide pointers for getting blood sugar into the normal range.