Low testosterone levels 'linked to chronic diseases'

"Men with low levels of testosterone are more likely to get a chronic illness," says the Mail Online, reporting on a US health survey.

The National Health and Nutrition Examination Survey looked at nearly 2,400 men during 2011-12, collecting information about their health and social background, and carrying out blood tests for a number of health indicators, including testosterone levels.

While it's common for testosterone levels to change over a lifetime, some men can end up with lower levels than other men of a similar age. This study found that men who were considered to have low testosterone levels for someone of their age group were more likely to have several health problems than those who had "normal" levels.

This study only looked at the men's health at a single point in time, so we can't draw any conclusions about what came first: the low testosterone or the health problems.

A number of lifestyle factors – such as smoking, obesity and eating a high-fat diet – are known to affect testosterone levels as well as chronic disease risk, so it could be the case that some or all of these factors are playing a role.

Measuring men's testosterone levels and general health over a longer period could help researchers better understand the link between low testosterone and poor health. It's currently unclear whether giving testosterone supplements to men would have any effect on their chronic disease risk.

Where did the story come from?

The study was carried out by researchers from the University of Michigan, the Malcom Randall Department of Veterans Affairs Medical Centre and the University of Florida.

It was funded by the North Florida/South Georgia Veterans Health System and published in the peer-reviewed medical journal Scientific Reports.

While the Mail Online's headline gave the misleading impression that low testosterone was shown to be a cause of poor health, the article itself clarified that the study had not shown a causal link.

What kind of research was this?

This was a cross-sectional study looking at men's health survey data, collected at a single point in time.

The data came from a large ongoing US study called the National Health and Nutrition Examination Survey (NHANES), which has been conducted annually since 1999. It collects questionnaire data as well as physical measurements of the participants, including blood tests such as cholesterol and glucose levels.

It's a well-established study involving large numbers of people, which means it's very useful for giving a snapshot of population health during each survey period.

However, people are not followed up, and the study is not designed to investigate a particular exposure-outcome question. As such, it cannot tell us whether some characteristics have caused others or if they just happen to occur side by side.

Also, rather than checking medical records, the survey relies on people telling the researchers about their health conditions, so it's possible some of the data on existing health problems might not have been accurate.

What did the research involve?

Researchers used data from the 2011-12 NHANES study because it contained data relevant to this question. The survey included 2,399 men, of whom 2,161 had complete data for this study.

The researchers looked at a range of characteristics, including:

• demographic factors like age, ethnicity and education
• body measurements such as height, weight, body mass index (BMI) and grip strength
• existing health conditions such as type 2 diabetes, arthritis, heart disease, lung disease, high blood pressure and depression
• blood pressure measurement and blood tests, including cholesterol, blood glucose and markers for diabetes
• testosterone levels, defined as "total testosterone", measured from blood samples

The researchers recorded health conditions, according to the men's self-reports of what they had been diagnosed with, and combined the data on age and testosterone level to categorise people as having low, medium or high testosterone based on what was typical for men of their age.

What were the basic results?

Across all men in the study, 30.8% had some degree of testosterone deficiency, and it was more common in older men than younger men.

Having more than one chronic health problem at once (multimorbidity) was more common in the men with testosterone deficiency (55.2%) than those with normal levels (36.6%). This pattern was seen both in younger and older men, but not in the middle-aged group.

For the older group, multimorbidity rates were very high in general – 75% in the testosterone-deficient group and 61.5% in the normal-levels group.

Among younger men, those with testosterone deficiency were far more likely to have obesity, diabetes, high blood pressure, high cholesterol and depression than those with normal testosterone levels.

How did the researchers interpret the results?

The researchers acknowledged it wasn't possible to tell from their study whether having low testosterone levels increased the risk of developing health conditions or whether having chronically poor health affects testosterone. They also noted it wasn't possible to find out whether other factors, such as diet or medication use, were influencing their results.

They said that further studies, looking at people over longer periods of time, would be useful for understanding how testosterone levels might affect whether men age healthily or not.

Conclusion

The finding that testosterone deficiency is more common in men with multiple chronic health conditions, particularly in younger men, is interesting.

However, this study does not tell us anything about whether low testosterone might cause general health problems or whether having a chronic health problem affects testosterone. If there is a direct link between the two, the reason for this is unclear. It might even be that something else is having a negative effect on both testosterone and other health problems.

For example, smoking might independently increase the risk of diabetes and cardiovascular problems (like high blood pressure and diabetes) and also affect testosterone levels. Similarly, obesity could be driving both the reduction in testosterone levels and the increase in chronic disease rates.

Longer-term studies following men over time would help us better understand whether there's a causal link between testosterone and chronic health problems, and the reasons for it.

For now, the best advice for a healthy lifestyle that may reduce your risk of chronic health problems, as always, is to aim for a healthy weight, eat a balanced diet, take regular physical activity, avoid smoking and moderate your alcohol intake.

Read more advice about staying healthy in later life.