Does testosterone under 600 ng/dL really raise disease and mortality risk?

What did @pa_courtney actually say?

The claim is specific: testosterone levels under 600 ng/dL are correlated with diabetes, low libido, depression, cardiovascular disease, fatigue, and erectile dysfunction. That's a high bar, since most labs flag "low" testosterone at 300 ng/dL or below. Setting 600 as the threshold implies a large chunk of men with technically "normal" levels are still at elevated risk.

To be fair, she said "correlated with" not "caused by," which is the right framing. Correlation claims are testable. Causation claims are harder. The distinction matters, and she mostly stayed on the right side of it.

Does the science back this up?

Partially, yes. The association between lower testosterone and cardiometabolic disease is real, but the 600 ng/dL cutoff is not a consensus clinical threshold. Most studies use cutoffs well below that.

The European Male Ageing Study (Huhtaniemi et al., 2012, Journal of Clinical Endocrinology and Metabolism) found increased metabolic syndrome risk at levels below roughly 400 ng/dL, not 600. A large meta-analysis by Araujo et al. (2011, Journal of Clinical Endocrinology and Metabolism) linked lower testosterone to all-cause mortality, but again, the meaningful threshold in that data was closer to 300-400 ng/dL. The Massachusetts Male Aging Study (Feldman et al., 2002, Journal of Urology) documented associations between lower testosterone and erectile dysfunction, though it did not endorse a 600 ng/dL floor.

Some functional medicine and longevity-focused practitioners do argue for "optimal" ranges above 500-600 ng/dL. That view exists in the literature, but it is not where mainstream endocrinology has landed.

What did they get wrong (or right)?

The conditions listed, including diabetes, depression, cardiovascular disease, and erectile dysfunction, are legitimately associated with low testosterone in the peer-reviewed literature. That part is accurate. The problem is the threshold.

Saying levels "under 600" are correlated with all these conditions is an overreach. It implies that a man at 450 ng/dL, which most labs would report as normal, is in a meaningfully elevated risk category. The data does not cleanly support that framing. The strongest associations cluster at the low end of the range, below 300-350 ng/dL.

There is also no mention of the fact that symptoms matter as much as numbers. Clinical guidelines from the American Urological Association and the Endocrine Society require both low levels and documented symptoms before diagnosing hypogonadism. A number alone does not a diagnosis make. Framing this purely around a numeric threshold, without that clinical nuance, could push men toward unnecessary testing or treatment.

What should you actually know?

Testosterone reference ranges are genuinely contested. The standard lab range of 300-1000 ng/dL is wide enough to drive a truck through, and there is legitimate scientific debate about whether the low end of "normal" is actually protective. Some researchers argue that optimizing toward the upper half of the range may have health benefits. That debate is real.

But real debate does not equal clinical consensus, and 600 ng/dL as a disease-risk threshold is not where the major guidelines sit. If your testosterone is 450 ng/dL and you feel fine, you are not necessarily in danger. If it is 450 and you have fatigue, low libido, and depression, that is a different conversation worth having with a clinician.

Total testosterone is also only part of the picture. Free testosterone, sex hormone binding globulin levels, and symptoms all factor into a proper evaluation. Anyone telling you a single number predicts your disease risk without those other variables is giving you an incomplete picture.