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28.04.2009

In primitive rural areas old men have just as much testosterone as young men

Once men pass the age of forty, according to endocrinology textbooks, their testosterone levels decline by one and a half percent each year. But this phenomenon is perhaps not as inevitable as we have been led to think, write American biologists in an article that was published in the American Journal of Human Biology. In the countryside of Bolivia, where conditions are almost medieval, older men have just as much testosterone as young men.

The testosterone level of older men can be thirty to fifty percent lower than it was when they were younger. The consequences include reduced muscle power, muscle mass and bone mass. But, nearly all data on ageing and testosterone come from men who are woken much too early every morning by an alarm clock, and then sit for hours in a traffic jam, making their way to a pointless boring job, living off a diet of ditchwater coffee from the machine. Yes, we're talking about men who live in industrialised society. But what about men living in societies where progress has not yet brought alarm clocks, traffic jams, pointless work and coffee machines? The researchers wanted to know this too, so they measured the testosterone levels in the saliva of 65 Bolivian men, living in the poor area to the south of La Paz.

The men's testosterone levels were higher in the morning than in the evenings, the researchers discovered. Same as with us. The researchers discovered as well, however, that there was no relationship between testosterone level and age. In the graph below the black circles represent the older men, and the crosses the younger men.

When the researchers looked at the date when the samples were taken, they noticed that the men's testosterone levels were much lower in the winter. It was the morning levels of testosterone that were lowest. Apparently the men's testosterone production did not increase during the winter nights.

Now winter in the Bolivian countryside is different from a mild West European winter. "The days are short, mean low temperatures are typically several degrees below freezing, and dust storms are not uncommon", the researchers write. "People may sleep longer, but perhaps less comfortably as fuels are too precious for most to use for heating homes. Food stores are declining, and many families are unable to purchase more foodstuffs. Documented responses to seasonal nutritional stress in the Andes include reduced activity levels."

Winter in Bolivia is gruelling. And that's why testosterone levels go down in winter. Maybe, the researchers suggest, this yearly cycle [of high testosterone levels in spring, summer and autumn, and a low level in the winter] stops the testosterone level from declining with age.

If this is the case, then men in industrialised society could keep their hormone levels up by going on a starvation diet during the winter and subjecting themselves for a couple of weeks to the freezing cold. Not pleasant, but apparently extremely healthy.

Source:
AAm J Hum Biol. 2009 Nov-Dec;21(6):762-8.

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