For most of human history, wealth has meant health - at least when compared with poverty. The rich of any society don't just live better than the poor, they live longer, and this was so even before there were effective medical treatments that the rich, but not the poor, could pay for.
So strong has the correlation been between wealth and health that we have come to expect that increasing incomes will translate into increasing lifespans, ad infinitum. But at the British Association for the Advancement of Science last week, Professor Andrew Prentice of the London School of Hygiene and Tropical Medicine pointed out that a steadily rising proportion of our children are grossly obese. Since obesity is the harbinger of a host of illnesses, some of which reduce life expectancy considerably, it is possible that we shall see a fall rather than a rise in life expectancy. Increasing wealth will not save us if we stuff ourselves with bad food.
I once had a practical lesson in the limitations of the association between wealth and health. It was in the little Pacific island of Nauru, which I used to visit regularly, and which for a time was the richest place per capita on earth, thanks to its phosphate rock, over which its inhabitants obtained financial control in 1968 from the British Phosphate Commission.
The islanders went suddenly from subsistence to great wealth. They could import all the labour they pleased, and avoid all work themselves. But their island, being only ten miles in circumference and its centre being a mined-out moonscape, offered little scope for distraction. Many passed the time by eating too much. Before long, the average consumption was 7,000 calories per day.
The Nauruans' taste in food was not sophisticated: indeed, it made McDonald's look like haute cuisine. They ate tins of Australian corned beef on huge piles of plain boiled rice, up to five times a day, which they washed down with Fanta: not just a tin, but a case of tins at a time. Those who liked alcohol as well as having a sweet tooth drank Chateau d'Yquem, of which there was an ample supply in the island's only supermarket.
Not surprisingly, the Nauruans became enormously fat. Half turned diabetic, and their life expectancy was about 47, much lower than that of populations with a fraction of Nauru's per capita income.
I am not suggesting that Britain is the new Nauru. Britain's ascent to wealth has been far more gradual and uneven than Nauru's. The Nauruans also had a genetic predisposition to diabetes, and with a population of only 4,000 surrounded by a wilderness of ocean, intermarriage on the island was inevitable. The predisposition became widespread.
Still, we are seeing the first generations in Britain in which inactivity and gross overeating are not only possible for a large number of the young but are unopposed by countervailing cultural pressures. Moreover, if you observe a British crowd walking along the street, it sometimes seems its members can hardly walk a few yards without refreshment. We have become a nation of Pooh Bears: with us, it is always time for a little something. We eat meals between sweets.
However, a statistical projection is not a prediction. Life expectancy in Britain may not decrease. In the intervening years, new treatments for the previously life-threatening consequences of obesity might become available.
So let us not be distracted from the real problem: an ageing population. In the meantime, we can be sure of only one thing: we shall either live too long, or not long enough.