Researchers at the University of Hawaii at Manoa have solved the mystery - why shorter men live longer.

Researchers discovered that a gene related to longevity, called FOXO3, is connected to body size.

Shorter men, characterised as 5-foot-2 or below, are more likely to have a protective form of the gene FOXO3, responsible for smaller body size during early development and a longer lifespan. These men also have enhanced insulin regulation and the ability to fight off cancer.

"This study shows for the first time that body size is linked to this gene," lead researcher Bradley Willcox said in a press release. "We knew that in animal models of aging. We did not know that in humans. We have the same or a slightly different version in mice, roundworms, flies, even yeast has a version of this gene, and it's important in longevity across all these species."

Residents from Honolulu, Hawaii have the longest life expectancy in the U.S. Besides longevity gene FOXO3, adopting a healthy diet and a physical activity program can also lead to longest lifespan.

For the study, the researchers observed the lifestyles of 8,006 Japanese-American men in Hawaii born between 1900 and 1919. The participant's information was provided by the Kuakini Honolulu Heart Program that started tracking men in 1965.

The participants were then divided into two groups - men with a height of 5.2 feet and shorter were assigned to one group and those who above 5.4 feet and taller allocated to the second group.

The researchers found that participants, who were 5.2 feet and shorter, were more likely to live longer. They had lower fasting insulin levels and had lesser incidence of cancer.

"The range was seen all the way across from being 5 feet tall to 6 feet tall. The taller you got, the shorter you lived," Willcox said.

From the study, 1,200 men of the 8,006 lived past the age of 90s and 100s. Nearly 250 of the men are still alive.

The finding is published in published in PLOS ONE.

A 2013 Yeshiva University study found that taller post-menopausal woman carry a heightened risk of developing cancers of the breast, colon, endometrium, kidney, ovary, rectum, and thyroid, multiple myeloma and melanoma.

"We were surprised at the number of cancer sites that were positively associated with height. In this data set, more cancers are associated with height than were associated with body mass index [BMI]," said Geoffrey Kabat, Ph.D., senior epidemiologist in the Department of Epidemiology and Population Health at Albert Einstein College of Medicine, in a press release."Ultimately, cancer is a result of processes having to do with growth, so it makes sense that hormones or other growth factors that influence height may also influence cancer risk."