Maintaining a healthy weight may mean more than looking good, according to a recent study — it may also help prevent breast cancer.

Women who gain 21 to 30 pounds after the age of 18 are 40 percent more likely to develop breast cancer than women who keep the weight off, the American Cancer Society reported after a nearly decade-long study on cancer and weight gain.

Heather Spencer Feigelson, epidemiologist with the American Cancer Society, said about 20 percent of women in the study gained at least 21 pounds after the age of 18.

“The more you gain, the higher your risk,” said Kerry Finnegan, spokesperson for the American Cancer Society.

Women gaining 70 or more pounds after the age of 18 are twice as likely to develop breast cancer, according to the study.

Finnegan said weight, along with family history and age, is one of the factors in cancer.

“We think that hormones tend to stimulate growth of cancer cells rather than actually cause a mutation,” said Larry Otteman, oncologist at the McFarland Clinic.

Autopsies have shown a variety of cancers people were not even aware of, Otteman said. This indicates the cancer may not be the problem, but the hormones that promote the cancer.

Research has linked higher estrogen levels to cancer risk. The heavier a woman is, the higher her estrogen level, Otteman said.

Insulin growth factor, a general cell stimulant, and estrogen increased with weight in women. Estrogen and insulin growth factor are both promoters, meaning they cause cells to grow more rapidly and divide more often.

“Initiators” and “promoters” are two categories of cancer cells, Otteman said.

“Anything that interrupts these hormones will reduce your risk of cancer,” he said.

Because women get estrogen by ovulating, not ovulating reduces one’s risk. Therefore, activities such as breast-feeding and pregnancy, which usually cause women to stop ovulating, reduce the risk of cancer.

Also, girls who start their menstrual cycle later in life can reduce the years they receive estrogen. The same is true for women who complete menopause earlier in life.

Otteman said weight gain can not only increase the risk of breast cancer, but increase the risk of it returning as well. He said the factors of diet and nutrition, child-bearing and inheritance play equal roles in risk.

Eunice Bassler, senior lecturer of food science and human nutrition, said women who are at a lower risk are those who eat a healthy diet and exercise frequently.

“We’re in a country where the most consumed vegetable is french fries,” Bassler said.

Eating fruits, vegetables and whole grains are important. She said the 18-to-24 age group is the most deprived of fruits and vegetables.

Finnegan said one-third of cancer in the United States can be attributed to diet and physical activity. Diet and physical activity are factors in risks for colon cancer, kidney cancer, and endometrial cancer, she said.

Although the correlation between weight gain and breast cancer is the only one that has been discovered, the American Cancer Society is looking into correlations between weight gain and other cancers, Finnegan said.

In Iowa alone, 2,320 new cancer diagnoses are made each year, and 430 people die each year from cancer, she said.