Does men's testosterone increase with age?

Question

It is generally thought that men's testosterone decreases with age.

However, according to Des Tobin, Professor of Cell Biology at the University of Bradford:

Surprisingly the levels of testosterone [in men] continue to increase with age up until the age of 70.

This is corroborated here:

For men, again the change in eyebrows is due to hormonal changes. For many their levels of testosterone remain at a good level or even continue to increase up to the age of around 70 and this can encourage vigorous hair growth particularly in areas that were perhaps not as robust in younger years – areas such as the nose, ears and eyebrows.

Given that both extracts mention the age of 70, are they perhaps referring to a single study?

Is Professor Tobin wrong?

Answer 1

One study argues the opposite, that testosterone drops with age:

In the present study in 890 generally healthy, middle class, American men in the BLSA, we found that both T and free T index (a calculated value related to free or bioavailable T) decreased progressively at a rate that did not vary significantly with age, from the third to the ninth decades.

To clarify their wording:

at a rate that did not vary significantly with age

they are saying that the rate of decrease is constant, that is T decreases linearly with age rather than exponentially or etc.

Source: "Longitudinal Effects of Aging on Serum Total and Free Testosterone Levels in Healthy Men", Endocrine Society - The Journal of Clinical Endocrinology & Metabolism

Answer 2

The body of accepted knowledge out there is that testosterone levels for men peak at 20 or shortly thereafter, and by the age of 30 is dropping at about 1% per year. While I'm sure there are exceptions, they are just that, not the rule.

Don't know what Dr Tobin is talking about.

Testosterone level chart

Answer 3

The best evidence indicates men's testosterone tends to DEcrease with age.

It's important to look at the quality of the sources. I don't think the sources in the OP are of the highest quality. Nor is the one used by PoloHoleSet! They're OK. But the Harman study HC_ uses is better - the "Confounds and validation" shows the effort they went to to ensure they had good data. It's peer reviewed. It's published.

Looking further, I found a review article which states,

Testosterone levels also decrease with age as rapidly as 0.4–2% annually after age 30 years [Harman et al. 2001; Kaufman and Vermeulen, 2005; Wu et al. 2008], with 35% of men in the seventh decade having lower testosterone levels than younger men [Vermeulen and Kaufman, 1995], and 13% of older age men meeting diagnostic levels for hypogonadism.

• source

Reading between the lines that follow, it seems like there's a needle being threaded - are the authors avoiding directly stating that if it's a normal part of aging, it can't be justified as medically necessary but lots of money is spent on T, so let's find a way to tell practitioners how to diagnose low T as a disease that merits treatment? Can't say. It's a matter of opinion. They later say, there's a "vast literature of known and proven benefits of testosterone normalization" but also quote the FDA saying ‘The benefit and safety of TRT/[testosterone replacement therapy] medications have not been established for the treatment of low testosterone levels due to aging, even if a man’s symptoms seem related to low testosterone.’

Hard to make any hard fast conclusions, given meta-analysis identified publication bias between industry-sponsored and unsponsored trials of testosterone supplementation!