What is the real reason for low libido in men?

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Increased body fat and decreased sexual desire in middle aged men may be a result of low levels of estrogen a new study shows.
Previously, a drop in testosterone production might have been suspected as the culprit, but researchers said a decline in estrogen may be part of the problem.
Traditionally, a diagnosis of male hypogonadism - a drop in reproductive hormones sharp enough to have physical effects - was based solely on a measurement of testosterone levels.
These diagnoses have increased dramatically in recent years - leading to five times as many testosterone prescriptions in 2000 as in 1993. Yet doctors understand little about the exact levels of testosterone needed to support normal function.
Testosterone production also has a direct impact on estrogen levels in men, since a portion of the male hormone is always converted into estrogen. That makes it hard to know which hormone is needed, and in what quantity, to counteract the symptoms that appear in older men.
To find out, researchers suppressed all natural hormone production among more than 300 male test subjects, aged 20 to 50. Half of the subjects were given a daily dose of a testosterone gel or a placebo for 16 weeks. The other half were given the gel plus a drug that inhibits the conversion of testosterone to estrogen.
The results of the study suggest that testosterone regulates lean body mass and muscle strength, while estrogen impacts the accumulation of body fat. And sexual function was impacted by both hormones: a lack of estrogen decreased desire, while a low level of testosterone impeded erectile function.
The study can be found in the New England Journal.

Study links obesity, heart risk

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A 30-year study finds the risk for heart disease rises the longer someone is obese.

Young adults who remain obese for two decades or more double their risk of developing a marker of heart disease in middle age, a study found.
Every year of obesity raises the risk of developing coronary artery calcification, a silent predictor of heart disease with mild to no symptoms, by two to four per cent, according to research in the Journal of the American Medical Association.
The study is the first to show that how long a person is obese can independently contribute to heart risk, said Jared Reis, the lead study author and an epidemiologist at the National Heart, Lung, and Blood Institute, which is based in Bethesda, Md.
In the new study, Reis' team used scans to track calcium buildup in the heart arteries in almost 3,300 adults 18 to 30 years old. When the study began in the mid-1980s, none of the participants were obese.
During the course of the study, however, more than 40 percent became obese and 41 percent developed abdominal obesity (excess belly fat). Those who became obese tended to stay obese for years, the researchers noted.
The investigators found that 27.5 percent of these long-term obese participants showed signs of heart disease, and the problem got worse the longer the individual had been obese.
More than 38 percent of those with more than 20 years spent obese had calcified arteries compared with only about a quarter of those who never put on that level of excess weight, the findings showed.
Among those with overall obesity, 6.5 percent had more dangerous "extensive" arterial calcification, as did 9 percent of those with obesity centered around the belly area. In contrast, only about 5 percent of those who were not obese had this extensive calcification, the researchers found.
Reis said the findings could have dire implications as Americans age.
"With the increased prevalence of obesity over the last 30 years, younger individuals are becoming more obese at a younger age than in previous generations," he noted. "This longer duration of obesity may have important implications on the future burden of subclinical heart disease and potentially rates of clinical heart disease in the United States."