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.

This Sexual Problem May Reveal a Weakened Heart

Impotence may signal heart disease.Men with increasingly severe impotence problems are wise to take immediate heart-healthy steps. That is because a new health breakthrough found that impotence is linked to a higher risk of heart disease and even death.
Published in PLOS Medicine, the large-scale study shows that the risk of future cardiovascular disease and death rises as erectile dysfunction (ED) becomes more severe. This is the case even for men with no history of heart problems. This is the first study to show that severity of impotence corresponds to a higher risk of heart disease hospitalization and all-cause mortality.
Australian researchers examined the link between severity of self-reported impotence and those issues in 95,000 men over the age of 45. It included more than 65,000 men without known heart disease, and more than 29,000 men with heart disease.
During two years of follow-up, there were 7,855 hospitalizations for heart disease, and after three years, there were 2,304 deaths. Researchers found that men who did not have heart disease but had severe ED had a relative 35% increased risk of hospitalization and a relative 93% increased risk of all-cause mortality. For men with heart disease and severe ED, the numbers were 64% and 137%, respectively.
The researchers say this is important, as it highlights the need to consider impotence in relation to a wide range of heart problems. They stressed that it is unlikely that ED causes heart disease. Instead, the culprits are conditions such as atherosclerosis (clogged arteries) that are contributing to both.
Most importantly, men who are experiencing significant impotence problems are wise to get some testing to assess their risk for heart disease. Meanwhile, making lifestyle changes to promote heart health is an important step.
based on:
This Sexual Problem May Reveal a Weakened Heart
Banks, E., et al., “Erectile Dysfunction Severity as a Risk Marker for Cardiovascular Disease Hospitalisation and All-Cause Mortality: A Prospective Cohort Study,” PLoS Med. 2013; 10(1): e1001372.