Last weekend was the World Science Festival in New York City. On the final day of this 5-day event there was a presentation on anti-aging called, 90 is the new 50. The theme of the talk was advances in anti-aging medicine with the bottom line message being that great advances is human longevity are right around the corner.

I certainly hope this is true, but I still take a sideways skeptical glance at such claims. Longevity research is a funny field in that it seems to me to be completely legitimate science and yet it cannot seem to get away from the whiff of pseudoscience that seems to surround it. Why is that?

Part of it, I think, is justified. But let me back up and put things into perspective. Modern medicine (including nutrition, sanitation, and medical treatments) has prolonged life expectancy from around 40 a century and a half ago to around 80 today. So, in essence, science has already produced a significant increase in human longevity. It seems reasonable to expect that this trend will continue as biology and medicine continue to advance.

On the other hand, however, there is a difference (often missed) between life span and life expectancy. Life span is the amount of time a healthy member of a specific species is likely to live if it avoids premature death by injury or bad luck. A healthy human can live 80-100 years before they die of “old age” – which usually means that their heart gave out or they had an inevitable acute illness they were not strong enough to survive. (Rare individuals can live past 100, with the very oldest getting to about 115.)

Life expectancy is different – it is a statistical statement about how long a member of a population is likely to live, on average. Therefore, a population may have a life span of 80 years but a life expectancy of only 40 years if dying young from disease or injury is common.

There is no question that modern medicine has increased life expectancy. People are much less likely to die, for example, when they are 20 from pneumonia than they were a century ago. The question is, however, has modern medicine increased the human life span – or are we just getting better at preventing and treating disease, and making life generally safer, so that people are more likely to live out their life span? In other words, are we currently pushing up against the upper limit of life expectancy? Perhaps we can eek out another 5-10 years, but we are getting to the point of diminishing returns as we run up against absolute biological limits.

This question is actually the scientific debate that is raging. Life extension advocates say that these biological limits to life span are all fixable (“death is an engineering problem”) while skeptics say that that they are too inherent and complex to impact significantly.

Both sides, in my opinion, have legitimate points. I come down somewhere in the middle. I think that radical life extension is possible, but perhaps more difficult than the proponents predict. As a physician my training has taught me that biology is extremely complex and it almost always turns out to be more difficult than we anticipate to see all the consequences of our interventions.

What increasing human life span (again, not just life expectancy) requires is not just reducing disease (although that will help) but also getting cells to survive longer and healthier. We need to address the fundamental causes of aging at the cellular and sub-cellular level. I don’t see any reason why this would be impossible, I just think it is going to be very difficult.

A great deal of the anti-aging research has been conducted so far on animals, such as mice and yeast. Significant life extension has been achieved, through calorie restriction and certain medicines, for example. This is offered as a proof of concept that such extension are possible in humans. However, animal models are imperfect, and I think that they are especially so with this question. I think it is very problematic to extrapolate from a survival measured in months to one measured in decades. The factors that limit the life span of a mouse may ultimately be very different than those for humans.

Predicting the future course of scientific development is always difficult. There may be unforseen breakthroughs, or we may find that a specific intervention works much better than anticipated. But it is equally likely that we will run into unanticipated roadblocks and be frustrated by a lack of progress. But (with that huge caveat) what I see as likely to happen is that many of the current lines of anti-aging research will bear some fruit. I think the human life expectancy will continue to rise in the short term, and that life span will be extended slowly, one step at a time. With current approaches I expect years, perhaps a few decades, of extension.

Beyond that, however, will likely require new technologies not yet in existence or even conceived of. This may include, for example, the ability to clone an entirely new body (except for the brain, of course, which will be the toughest nut to crack). Will such radical new technologies all predictions are null and void – almost anything is possible.

But what about right now? At present there is no magic pill or treatment that will make you live longer. In an interview about the conference, participant David Sinclair advised people who want to live longer to “exercise.” I completely agree with this advice and want to add to it.

While fancy supplements and interventions may eventually increase life span, right now people are better served focusing on what is known. Avoid obvious risk factors for disease, like smoking and excessive alcohol. Exercise regularly, and eat a well-balanced diet. Get basic medical monitoring and preventive care. You could do more for your health and longevity with these basic lifestyle changes than all that longevity science currently has to offer.