A large study involving almost 160,000 people has suggested that low testosterone in older men has a link to dementia and Alzheimer's disease. The researchers did not find a causal link, so the nature of this relationship is not known, but the paper is one of the sturdiest pieces of evidence that has highlighted this connection yet.
The research was recently published in the journal Alzheimer’s and Dementia. Scientists led by the University of Western Australia in Perth sifted through data from the UK Biobank, an open-access biomedical database containing in-depth genetic and health information from half a million people in the UK. From this repository of data, they looked at 159,411 men aged between 50 and 73, up to 826 of whom had developed dementia, including 288 with Alzheimer’s disease.
After adjusting for other variables, they found that the older men with lower testosterone were significantly more likely to have dementia and Alzheimer’s disease.
Testosterone is the male sex hormone associated with sex drive, muscles, aggression, and sperm production. Women also produce testosterone, but at significantly lower levels than men.
The question remains, is this link with dementia just a coincidence, does testosterone protect against dementia, or is another factor at play? The researchers aren’t sure, but this isn't the first time a link has been found. A strong number of studies have highlighted this relationship in recent years. It’s also noteworthy that the majority of people living with Alzheimer’s are women, further hinting that testosterone may have some kind of a protective effect.
On the other hand, some researchers have previously said the findings from these studies have proved inconsistent and there’s not enough data to draw study conclusions just yet. An investigation in 2017 looked to see whether testosterone treatment improved the memory and cognitive functions of older men with low testosterone, but they concluded it had little to no effect.
It’s more certain that low testosterone can cause other problems for men, including low libido, erectile dysfunction, loss of muscle mass, reduced bone mass, low mood, and lack of energy. It’s hard to know how common low testosterone is because it’s very hard to measure. Levels of testosterone can vary throughout the day and can be influenced by other factors, like alcohol use, age, diet, certain medications, and illness. One estimate says a total of 2 percent of men have low testosterone, but it may affect up to 40 percent of men aged 45 and older.
Worryingly, low testosterone also appears to be on the rise among young men. A significant 2007 study found a “substantial” decline in men's testosterone levels in the US since the 1980s, with levels equivalent to a drop of 1 percent each year. The reasons behind this slump are not clear, but it’s thought to be a symptom of industrialized lifestyles, from sedentary jobs to bad diets.