Free The Lucky Years: How to Thrive in the Brave New World of Health by David B. Agus

ideas are difficult to test experimentally and remain conjecture. But in all the years of debating the topic, we’ve forgotten one important part of the equation: the male versus female stem cell.
    Because one of the hallmarks of aging is the decline of stem cells’ functionality, we must ask whether the aging of stem cells differs between men and women, and whether this has consequences for disease and life span. Studies thus far have shown that some stem-cell populations in females are superior to those in males thanks to estrogen, the female sex hormone. Stem cells destined to be blood cells, for example, are more abundant in female mice than in male mice, an effect that is dependent on estrogen signaling. A similar paradigm has been described in neural stem cells where estrogen increases the proliferation of these cells in a transient manner that fluctuates throughout the menstrual cycle.
    Estrogen signaling is not the sole contributor to differences in stem-cell regulation between the sexes. Other studies have shown that females also exhibit increased capacity for rapid wound healing and liver regeneration, processes that are likely dependent on resident stem-cell populations. So females tend to show increased stem-cell self-renewal, regeneration potential, and in some cases, proliferation. But the big question remains: Does this tendency toward increased self-renewal in females alter the capacity of stem cells to regenerate tissues throughout aging? Does it actually influence longevity?
Do Telomeres Tell a Story?
    In recent years, we’ve also heard a lot about telomeres, which are the strands of DNA at the ends of chromosomes. Because they protect our genetic data and make it possible for cells to divide, they’ve been hailed as a linchpin to health and are believed to hold some secrets regardinghow we age and develop disease. But despite the initial excitement for measuring telomeres and drawing strong correlations—shorter telomeres and shorter life—the evidence has been decidedly mixed and confusing. In fact, a 2015 study in Human Molecular Genetics, using data from 50,000 cancer cases and 60,000 control cases, showed that the longer your telomeres were, the higher the risk for lung cancer. 17 The role of telomere length in health will be a complicated one, and it is too early now to know its meaning.
    While telomere shortening has been associated with the aging process, we don’t know yet whether shorter telomeres are just a sign of aging, akin to gray hair and wrinkles, or whether they actually contribute to aging. Those are two very different things. Once we figure out why gender can be such a factor in the aging process, it’s possible we’ll no longer look at telomeres in the same way, which may be reflecting how fast one is aging and not commanding the process.
Holding On to Optimism
    If you’ve ever been to a school reunion, you’ve seen the difference between those who have become fat and bald before their time and the ones who look like they haven’t aged a day since you last saw them. I can’t tell you how many times I meet couples of the same age who look vastly different in their physical “age.” And what I find most striking is that nine times out of ten, the younger-looking individual has something else that’s not nearly as present in the “older” person: positivity. Optimism. An upbeat personality, a perspective that sees the glass as half full.
    It’s cliché, but it’s true: having a positive outlook about the world and even the future of medicine is key to health. I see it every day in my practice, even among those who are prone to depression and do what they can to manage it successfully. And it’s easier to be optimistic if you remember that breakthroughs are about to happen in many areas of medicine (not just oncology) that will change how you engage with doctors and how you live.
    A great example of a new technology that will soon change our lives and help us to