January 28, 2011
Dear Mayo Clinic:
I have read various studies that suggest sugar can cause cancer. I was diagnosed with cancer two months ago and a dietitian advised me to avoid sugar. Is there a connection between sugar and cancer?
This question doesn't have a clear "yes" or "no" answer. Sugar alone doesn't cause cancer. Eating too much sugar, though, can lead to other conditions associated with an increased risk of cancer. If you're trying to reduce your cancer risk, the best strategy is to make healthy lifestyle choices, including limiting sugar consumption.
A common concern of patients is that sugar causes cancer or causes cancer to grow faster. Various studies have looked at this question. The results have found a loose association between elevated blood sugar (glucose) and cancer. But these findings don't mean that sugar causes cancer. It's not that straightforward.
Instead, it's important to look at diet in the big picture. For example, consuming large amounts of sugar every day can cause health problems. But the sugar isn't automatically associated with cancer. Too much sugar can, however, lead you to be overweight, become obese or develop diabetes, which results in high blood glucose levels. And research has shown that postmenopausal women who are overweight, and who have been previously diagnosed with cancer, have a higher risk of cancer recurrence than similar patients who are at an ideal body weight (a body mass index of less than 25). So even though sugar does not increase your cancer risk directly, the effects of sugar consumption could increase the risk of cancer recurrence.
The same type of association pertains to many areas of nutrition and health. For example, alcohol doesn't directly cause cancer. But studies have shown that drinking on average more than one alcoholic beverage a day increases a woman's risk of developing breast cancer. That means a person can enjoy alcohol occasionally, but too much may increase cancer risk.
Another example is breast-feeding. Health care providers strongly advise new mothers to consider breast-feeding, not just for the benefits to the baby, but also because research has shown that breast-feeding reduces a woman's risk of developing breast cancer.
The point is that lifestyle choices are key. Generally, a lifestyle that's heart healthy will help protect you from cancer, too. That lifestyle consists of exercising for at least 150 minutes each week, quitting smoking, managing stress and eating a healthy diet — typically one that includes whole grains; lean meat, poultry and fish; and at least five servings of fruits and vegetables a day.
When considering cancer risk, determining what does and does not cause cancer can be complicated and confusing. Many stories on the Internet and in popular media include data that has not been verified scientifically and is based only on a few experiences or on limited observations. Even a scientifically controlled, randomized clinical research trial can't always show us the whole picture. Often, a group of studies analyzed together over time is necessary to accurately provide the data researchers are seeking. Even then, that information doesn't always apply to everyone.
If you're concerned about risk of cancer or cancer recurrence, talk to your doctor. He or she can help assess your cancer risk and find ways that may help minimize that risk. If you're looking at diet, risk reduction typically doesn't mean eliminating an entire category of food, such as all sugars. Instead, actively pursuing a healthy lifestyle is your best bet.
— Amber Isley, M.D., Family Medicine, Mayo Clinic, Jacksonville, Fla.