Loss of kidney function in old age is not inevitable

AS PEOPLE get older, their kidneys concentrate urine less effectively. Since, like most things, kidneys might expected to deteriorate with the passage of time, this is no great surprise. Yet a study just published in the American Journal of Physical Anthropology by Asher Rosinger of Pennsylvania State University suggests this notion is wrongheaded. Dr Rosinger has found that hunter-gatherers in Africa and forager-horticulturalists in South America are able to produce, into their seventies, urine which is just as concentrated as that of those in their twenties.

Monitoring urine concentration matters because, as the kidneys’ urine-concentrating ability diminishes, so too does their ability to filter out toxins and waste products from the blood. Eventually, this can force those with poorly functioning kidneys to undergo painful, expensive and time consuming dialysis.

While studying the literature on the matter, Dr Rosinger noticed that all relevant research had taken place in industrialised countries. Aware that past work with non-industrialised populations had shown that some conditions long thought to be age-related and inevitable, such as declining cardiovascular function, were not, Dr Rosinger decided to look similarly at kidney function.

He and his colleagues examined the urine-concentrating ability of 15,055 American adults who were neither pregnant nor suffering from kidney disease. In particular, they measured urine’s specific gravity. They then compared the specific gravities of their American samples with those of samples from 116 adult Tsimane, living in the lowlands of Bolivia, and 38 Hadza, living in Northern Tanzania.

As they expected, the density of American urine dropped significantly with the age of its producer. That of Tsimane and Hadza urine, however, did not. In fact, it remained unchanged. Kidneys do not appear to wear out, then, when operating in a context similar to the one in which human beings evolved. Precisely what it is about the modern, developed world which causes kidneys to deteriorate remains unclear. But if that thing could be identified, and proved tractable to treatment, then dialysis might become a thing of the past.