What causes low testosterone?

Low testosterone usually comes from a mix of lifestyle, age, and sometimes medical causes — and for many men, the biggest drivers are the ones they can actually change.

The most common contributors are everyday ones: carrying excess body fat (fat converts testosterone into oestrogen), poor or too little sleep, chronic stress and high cortisol, a sedentary lifestyle with little muscle, heavy alcohol use, and deficiencies such as low vitamin D or zinc. Testosterone also declines naturally with age — roughly 1% a year from the late thirties — but a lot of what men blame on age is really these lifestyle factors stacking up.

Then there are medical causes worth ruling out: type 2 diabetes and insulin resistance, an underactive thyroid, untreated sleep apnoea (strongly linked to low testosterone), certain medications (including opioids and some steroids), and — less commonly — problems with the testes or with the pituitary gland that signals them. Anabolic steroid use is a major and often hidden cause, because it shuts down your own production.

What to do: start with the fixable basics — lose excess fat, sleep well, lift weights, manage stress, moderate alcohol, and correct any deficiencies — and give them a few consistent months. If symptoms persist despite genuinely doing the work, that's the point to see a doctor for a morning blood test and to check for the medical causes above, rather than guessing.