Men who ride bicycles may experience hormonal imbalances that could affect their reproductive health, researchers say in a UCLA School of Nursing study released Monday.
To date, an extensive amount of research has been performed documenting the positive effects of long-term exercise on health, according to a nursing school statement.
"These studies have shown that while moderate exercise can lead to enhanced cardiovascular and metabolic function and reduced body fat, ultra-endurance levels of exercise can also adversely affect the neuroendocrine system and reproductive health," the statement said.
The UCLA study explored the associations between exercise intensity and circulating levels of reproductive hormones in serious leisure male athletes—triathletes and cyclists—and recreational athletes.
UCLA researchers, according to the nursing school statement, studied 107 healthy male athletes, ages 18 to 60, and divided them into three groups: 16 were triathletes, 46 were cyclists and 45 were recreational athletes. Blood samples were collected from each participant to measure total testosterone, estradiol, cortisol, interleukin-6 and other hormones.
"Plasma estradiol and testosterone levels were significantly elevated in serious leisure male cyclists, a finding not previously reported in any type of male athlete," said School of Nursing assistant professor Leah Fitzgerald, the study's senior author.
Plasma estradiol concentrations were more than two times higher in the cyclists than in the triathlete and recreational athletes, and total testosterone levels were about 50 percent higher in cyclists than in the recreational athletes, she said, adding, "These effects were accompanied by little or no compensatory shift in circulating reproductive hormone levels."
Estradiol is a form of estrogen and produced in males as an active metabolic product of testosterone. Possible conditions associated with elevated estrogen in males include gynecomastia, which can result in the loss of male pubic hair and enlarged breast tissue.
"Although preliminary, these findings warrant further investigation to determine if specific types of exercise may be associated with altered sex hormone levels in men that could affect general health and reproductive well-being," Fitzgerald said.
The study also found an association between an increase in estrogen levels and of chamois cream use, particularly for male cyclists using the cream for more than four years. But no direct cause and effect has been established, the statement said. The cream is applied to help prevent chaffing and bacterial infections related to bicycle saddle sores.
The UCLA study, "Reproductive Hormones and Interleukin-6 in Serious Leisure Male Athletes," was published in the European Journal of Applied Physiology. It was funded by the UCLA School of Nursing, UCLA General Clinical Research Center and the nonprofit Kaiser Foundation.
