So how long humans can actually live?

Many of us are wondering how long we can live?! Is there any way to be young longer? 
In the recent 50-60 years the life span has extended, but is often surrounded by many age-related diseases. Could the sequencing of the human genome and the recent discoveries in the genetics help us live a longer, and healthier life?

I have read an interesting interview with two of the leading scientists in the field of human ageing, where they answer these questions:
Lenny GUARENTE, PH.D.is a professor of biology at M.I.T. and author of "Ageless Quest: One Scientist's Search for Genes That Prolong Youth". 
Robert N. BUTLER, M.D. is a founding director of the National Institute on Aging, a founder of the Alzheimer's Disease Association and winner of a Pulitzer Prize in 1976 for "Why Survive? Being Old in America." He heads the International Longevity Center.; SARA DAVIDSON: Author, most recently, of "Leap! What Will We Do With the Rest of Our Lives?"

Here are some of the most interesting parts of the interview with the journalist Sara Davidson, published in the New York Times. 

Dr. GUARENTE, scientists like J. Craig Venter, one of the first to map the human genome, feel that increasing life span should not be the goal of science. Why are you attempting to prolong life?

LENNY GUARENTE: The research that I’m involved in is not about extending life after people are infirm. I don’t think of life span as the gold standard. The gold standard is health span. All the indicators from the laboratory are that the genes we’re studying and the kinds of drugs we would be developing would extend health span. If you can extend health span, and you also happen to extend life span, so be it. That’s a side benefit.

Have you identified genes that can extend health and life span?

GUARENTE: The genes we study counteract aging. First we studied yeast cells, and it took us eight years to identify a gene called SIR2, which protects the cells from damage during the aging process. Then we did a similar experiment in a more complex critter, the roundworm, and what was remarkable is, we identified the same gene. That told us that this type of gene is performing an antiaging function broadly in nature.

Do humans have this gene?

GUARENTE: There’s one gene in our genome, SIRT1, that would be a dead ringer for this one — the technical term is ortholog — but we also have six other genes that have a related sequence to this. They’re called sirtuins, and they’re all going to play a role, but I think the dead ringer is undoubtedly the most important based on experiments that have been done.

You assert a fairly radical concept: that these longevity genes have the power to keep the body supercharged and maintaining its natural repair activities regardless of age. Does that mean we could live, what, another 20, 30 years? Fifty?

GUARENTE: We think the sirtuin genes are there to recognize lack of food or other stressful situations and to spring into action to create a physiology that will promote longevity. The evolutionary value is that in times of stress — food scarcity, for example — this gene would slow down the aging process and keep you alive longer, so that when times are better, you could reproduce.

But how long would the gene work? Maybe it only operates temporarily?

GUARENTE: We can gauge this by asking what happens in rodents on a calorie-restricted diet, which mimics food scarcity and activates the SIR2 gene. Do they live forever? No. They live up to 50 percent longer. So in a perfect world, one would hope that we could live 50 percent longer than the current expected life span.

In our lifetimes, could this happen?

GUARENTE: I think one can expect perhaps another decade of robust health.

ROBERT BUTLER: A lot of it comes down to our willingness in this country to make an investment in the biology of aging. Historically, we’ve devoted our energies and money to studying one disease at a time. At the same time, we have neglected targeting the underlying risk factor of aging.

Are you saying that aging itself leads to disease?

BUTLER: Why does 50 percent of all cancer occur after 65? Why does 80 percent occur after age 50? As we age, there are changes at the cellular molecular level that predispose us to disease and disability. But so far, no government, no foundation, no corporation anywhere in the world has fully embraced the importance of longevity science. If we could target aging, that would have an impact on diseases.

What do you mean “target” aging?

GUARENTE: Slow down aging in the same way that calorie restriction slows down aging. Bob makes an important point about diseases and aging. I believe that the two are intertwined and experimentally this has been demonstrated by using modern strains of mice that have been genetically altered to get specific diseases — for example, neurodegenerative diseases or cancer, or cardiovascular disease or diabetes — and to see whether calorie restriction will either postpone or prevent these diseases. The general finding is that calorie restriction forestalls many of these diseases. The hypothesis is that if one could activate the sirtuin genes — not by a calorie-restricted diet but pharmacologically — then this would have an impact on the diseases of aging.

How close are we to such a drug being available?

GUARENTE: Ten, maybe 15 years. I think the drugs that aim at sirtuins, for example, will be tested initially for a particular disease, say, diabetes. And it will turn out that the drugs have broader benefits than one initially imagined.

There are substances on the market now that claim to prolong life — and people are spending billions on them. What’s the distinction between these products and the drugs that you’re hoping to develop?

GUARENTE: Well, that’s really simple. Any product on the market that claims to extend life — don’t believe it.

BUTLER: That’s true. We don’t yet have the means to delay, stop or reverse aging. And in fact, we don’t even have the means to evaluate or measure whether a substance prolongs life. We have yet to create biomarkers that would measure, short of death, actual changes in the body that reflect aging.

Let’s talk for a minute philosophically. What kind of society will we have if everybody is living to 100, and the whole culture skews older?

BUTLER: You could have asked that same question in 1900, when the average life expectancy was 47. Someone might have said, what are we going to do when we have all these 55- and 60-year-olds around? Society adjusts. People think we can’t afford older people because of Social Security and Medicare. But there’s a growing body of knowledge by hard-nosed economists of all ideological persuasions — University of Chicago, Yale, Harvard, the RAND Corporation — that as societies become more long-living and healthier, that actually creates greater wealth. Bloom and Canning up at Harvard have shown that if you identify nations that have a five-year difference in life expectancy, the one that has a greater life expectancy also has greater wealth. Older people create silver markets, so that one person’s cost, like health costs, is another person’s income, asset or job.

What about the institution of marriage? If you’re going to live to 100 and get married at 22 or 25. ...

BUTLER: Oh, you are evil.

Are you still going to vow “till death do us part”?

BUTLER: There’s a demographer, Peter Uhlenberg, who said that divorce is a substitute for death, because in the old days there was enough death, unfortunately, particularly of women in childbirth, that the men would remarry. Someone even calculated that marriage now lasts about as long as it did then, but it was ended then by death rather than by divorce. So maybe you’re onto something.

Are you concerned that extending life span could double the number of people alive and overwhelm the planet’s resources?

GUARENTE: I don’t believe that mitigating the diseases of aging will lead to overpopulation, because in most of the developed world birthrates are low or declining.

BUTLER: They’re falling in the developing world as well. There’s a distinction between advancing life expectancy and breaking the genetic barrier. Every species has a predetermined genetic life span. Certain fish live about a year. Some turtles live 200 years. Humans have about 110, 120 years at the outside of their genetic life span. We’re talking about increasing healthy years within that life span.