Mortality May Be Highly Plastic

Mortality May Be Highly Plastic
Even at Advanced Ages
It's never too late to whisper words
Concerning the way of bees and birds.
It’s never too late to fall in love.
— Sandy Wilson, The Boyfriend

o date, dietary restriction has been a sure-fire way to prolong survival and increase maximum lifespan in organisms from yeast to mammals—possibly even in primates and humans. However, dietary restriction is a valuable strategy only if it’s begun early in life—or at least “midway” through life—and continued rigorously until the end of all your days. Right?

Wrong, if we are to extrapolate from a recent study done with fruit flies.1 In this study, dietary restriction was found to extend lifespan solely by reducing the short-term risk of death, independently of whether the flies had previously been on a restricted diet, and independently of the point at which the restriction was begun. This finding conflicts with the idea that a lifetime of abstinence is required to reduce one’s risk of death. It also appears to conflict with the idea that dietary restriction works by reducing wear and tear.

In the study, two days after dietary restriction was instituted for the first time, at any age, previously fully fed flies—never before on dietary restriction—were found to be no more likely to die than flies of the same age that had been subjected to long-term dietary restriction. In other words, flies that began dietary restriction at some later point in life, even quite late in life, were just as well off as those that began dietary restriction at birth.

If these results hold up, the start of dietary restriction late in life may reduce the short-term risk of death so that it is equal to that of lifelong dietary restriction. Then dietary restriction instigated at any age could generate a full reversal of mortality—in fruit flies, anyway.

In the broader perspective, the findings of the fruit fly study raise the greater question of what determines longevity—not just in fruit flies, but also in humans. Since demographers have determined that age-related death rates in humans are determined by conditions and behaviors of the present, more than those of the past, could it be that mortality is highly plastic, even in old age?

In other words, “It’s never too late.”2 Which may be enough to encourage you to hang on to your life, for, ipso facto, you might find that the gift of longer life is just around the corner. In keeping with Robert Heinlein’s great paean to longevity, “Time Enough for Love” (and with apologies to Sandy Wilson):

It’s never too late for increased lifespan,
And suddenly becoming as well as you can.
It’s never too late to fall in love.

References

  1. Mair W, Goymer P, Pletcher SD, Partridge L. Demography of dietary restriction and death in Drosophila. Science 2003 Sep 19;301(5640):1731-3.
  2. Vaupel JW, Carey JR, Christensen K. It’s never too late. Science 2003 Sep 19;301(5640):1679-81.

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