What causes low testosterone?

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

The everyday contributors do most of the damage:

• Excess body fat, which converts testosterone into oestrogen and feeds a downward loop
• Poor or too little sleep, since most testosterone is made during deep sleep
• Chronic stress and high cortisol, which directly opposes testosterone
• A sedentary life with little muscle
• Heavy alcohol use
• Deficiencies such as low vitamin D or zinc

Body fat deserves singling out, because it sets up a self-feeding cycle: fat tissue carries the enzyme aromatase, which turns testosterone into oestrogen, and lower testosterone then makes fat easier to gain. Break that loop and a lot of the rest eases. Testosterone also declines naturally with age, by roughly 1 per cent a year from the late thirties, but a great deal of what men blame on age is really these lifestyle factors stacking up. The encouraging flip side is that they are the ones you can move, which is why raising testosterone naturally starts here, and why sleep in particular matters so much.

Then there are medical causes worth ruling out: type 2 diabetes and insulin resistance, an underactive thyroid, untreated sleep apnoea, certain medications including opioids and some steroids, and, less often, problems with the testes themselves or with the pituitary gland that signals them. Blood tests of LH and FSH help tell those two apart. Anabolic steroid use is a major and frequently hidden cause, because it shuts down your own production, sometimes for a long time.

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 is the point to see a doctor for a morning blood test and to check for the medical causes above, rather than guessing.