Are Testosterone Levels in Men Really Declining?

The short answer

Yes, the weight of evidence says average testosterone in men has fallen over recent decades, and not only because men are living longer. Several large studies compared men of the same age measured in different years and found that the later groups had lower levels.

What is less clear is why, and how much of the drop is real biology rather than heavier bodies and changing lab methods. The answer matters less for headlines than for one practical point: your own number has to be measured carefully and read against your symptoms, not against your father’s.

What the Massachusetts Male Aging Study found

The study that started the conversation followed randomly selected men aged 45 to 79 in greater Boston. Researchers drew blood starting in 1987 and again in two follow-up waves, in 1995 to 1997 and 2002 to 2004, collecting 2,769 measurements from 1,532 men.

When they analyzed the results in a 2007 paper, they found what they called a substantial, age-independent decline in testosterone over calendar time. In plain terms, a 60-year-old measured in the early 2000s tended to have lower testosterone than a 60-year-old measured in the late 1980s. The authors reported that the drop could not be explained by changes they measured in health and lifestyle, including smoking and obesity, and that the population-level fall was larger than the decline usually linked to aging itself.

They offered two broad explanations: differences between birth generations, or health and environmental factors the study did not capture. Nearly two decades later, that is still roughly where the science sits.

Has the same thing been seen elsewhere?

Several later studies from different countries point the same way, with different degrees of certainty.

The Israeli analysis is the most recent and the largest, drawn from routine tests at a national health organization. The U.S. survey study matters because it looked specifically at younger men, a group earlier work had largely skipped.

How much does weight explain?

Some of it, and the studies disagree on how much. Higher body fat lowers testosterone, partly by reducing SHBG, the protein that carries much of the hormone in the blood, and partly by suppressing the brain’s signal to the testes. Since average weight has risen over the same decades, obesity is the obvious suspect.

The Danish study gives the most interesting answer. In the Danish surveys, adjusting for the rise in body mass index made the drop in total testosterone shrink to the point of no longer being statistically significant, while the drop in SHBG remained. Free testosterone, the fraction readily available to tissues, did not show an age-independent change. The authors suggested that SHBG may have shifted first and total testosterone followed, settling lower to keep free testosterone steady.

The Boston, Israeli and U.S. studies, by contrast, found declines that persisted after accounting for weight. So weight is part of the story, probably not all of it. Our page on obesity and low testosterone looks at that link, and the article on whether weight loss raises testosterone covers what happens in the other direction.

Could the tests themselves have changed?

Yes, and this is the least discussed part of the debate. Testosterone has been measured with many different lab methods over the years, and they do not always agree. When researchers built harmonized reference ranges in 2017, cross-calibrating four large cohorts against a CDC reference method, they concluded that a substantial share of the variation between cohorts was due to assay differences rather than real differences between men.

That cuts both ways. Older measurements may not be directly comparable with newer ones, which makes some of the decline uncertain. But it also means the trend has now been seen across different methods, countries and decades, which makes it harder to dismiss as a lab artifact. The same 2017 work produced a harmonized range of 264 to 916 ng/dL for healthy, non-obese men aged 19 to 39 on calibrated assays, which is where the widely used 264 ng/dL figure comes from.

What it means for one man’s number

A falling average is interesting, but it does not change how an individual result is read. A few practical points follow from the research:

• Timing matters. MedlinePlus notes that testosterone is usually highest in the morning, which is why guideline diagnoses rely on early-morning draws. Our page on morning testosterone test timing explains the window.
• One result is never enough. Two separate early-morning tests are the standard before calling testosterone low.
• The lab method matters. If you compare results over the years, use the same lab where possible, or one that uses a standardized method.
• Age-based charts are a rough guide. Ranges by decade, like those on our page about normal testosterone levels by age, describe averages, and averages are exactly what has been moving.
• Symptoms still decide. A number near the low end with no symptoms is handled very differently from the same number with low libido, fatigue and loss of morning erections.

For younger men, it is worth knowing that low testosterone in your 20s and 30s has specific causes worth looking for; our article on low testosterone in men under 40 covers them.

How Ultimate Male measures testosterone

Whatever the population trend, your care is built on your own results. Through our preventative blood testing at San Gabriel and Downey, blood is drawn on site in the morning and results come back in 24 to 48 hours. The TRT pre-screening panel covers total testosterone, estradiol, PSA and a complete blood count, and your provider adds free testosterone, SHBG or LH when the picture calls for them.

A PA-C or MD reads the numbers with you alongside your symptoms, weight, sleep and medicines, and repeats any borderline result before drawing conclusions. If you are curious where you stand, start with the free 10-minute phone call at 626-319-5261.