U.S. researchers claim that a proper diet and exercise enhance body weight and physical function in seniors fighting with cancer.

The study, presented at the seventh annual American Association for Cancer Research Frontiers in Cancer Prevention Conference, confirmed early research showing that people who exercise regularly have a considerably lower risk of developing cancer.

But these benefits vanish if people sleep less than 7 hours per night, scientists say. They found a 47% increased risk of developing cancer in such people, compared to those who got more sleep. "We think it's quite interesting and intriguing. It's kind of a first look into this. It isn't something that has been widely studied," said James McClain of the National Cancer Institute.

There is evidence that exercise also reduces blood levels of estrogen and testosterone, two sex hormones produced in both men and women that have been linked to uterine lining, prostate and breast cancers. What’s more, exercise burns fat, which can store extra quantities of estrogen. And, as previous studies have shown, an elevated level of estrogen increases breast cancer risk. So by decreasing obesity, it reduces the risk of a series of cancers.

While researchers have an explanation for the impact of regular physical activity on cutting the risk of cancer, they have no idea about why an insufficient amount of time makes people more likely to develop the disease.