Being overweight predisposes the body to heart disease, but that's only one way that obesity can affect longevity and accelerate aging. New research suggests that it also makes cells older on a molecular level. For instance, some of the same researchers that looked at telomere length in active and sedentary twins also looked at telomere length in obese women. What they found was that obese women had shorter telomeres than lean women. If you translated the telomere length into years, the obese women's cells were nine years older than the lean women's. Excess body fat is also thought to cause oxidative stress and is known to promote inflammation of the kind that's been linked to age-related diseases.
Inflammation caused by excessive body fat may also be related to the shrinking of the brain. Gary Wenk, PhD, a professor of psychology, neuroscience and molecular virology, immunology and medical genetics at the Ohio State University and Medical Center, has shown that proteins that are a byproduct of inflammation can cause regions of the brain responsible for memory and learning new things to become smaller. Other studies have shown that older people who are obese have lesser cognitive and memory capabilities and are at an increased risk for Alzheimer's disease.
Another way that obesity affects aging is by contributing to insulin resistance. Insulin is the hormone charged with ushering the sugar from your blood into cells throughout your body. When you aren't producing enough insulin, or your cells become resistant to insulin's actions, blood sugar rises. People with type 1 diabetes produce no insulin. People with type 2—the kind that is often caused by too much body fat and constitutes about 90 to 95 percent of diabetes cases—are insulin resistant. That is, their bodies don't respond properly to normal amounts of insulin so that sugar doesn't get adequately transported from the blood to the cells. People with type 2 diabetes may even eventually stop producing normal amounts of insulin, which can make the situation worse.
Insulin resistance can shorten your life span and hasten aging in a number of ways: it encourages inflammation, quashes sirtuin activity (sirtuins are enzymes that delay cell death), shortens telomeres and raises levels of compounds called AGEs—advanced glycation end products—that wreak havoc in the body. Besides obesity (and particularly an overabundance of intra-abdominal fat—stored fat that surrounds the organs), a diet high in sweets, sodas and other sugary drinks, white bread, white rice and other processed grains seems to promote insulin resistance. There's a hereditary factor to insulin resistance as well—your genes may make you more susceptible. But you might be able to stave it off for longer, and if you get it, regulate your blood sugar better, with the type of diet you'll find in chapter 3.
While the link between excessive body weight and aging is disheartening given the rates of obesity in this country, it's somewhat more surprising than what has long been known as the number one cause of preventable death: smoking. Besides its deleterious effect on life span, smoking promotes aging in just about every way imaginable. It's known, for instance, that smoking creates free radicals and that it's associated with the development of many age-related diseases, including some that you might not even think would be related: osteoporosis, diabetes and the eye disease macular degeneration. In the obesity study I mentioned earlier, they also looked at the effect of smoking on telomeres and found that it shortened telomere length by a full 18 percent.
It's been known for some time that smoking is linked to dementia, and recently researchers at Kaiser Permanente in Oakland found that it's also associated with an increased risk of Alzheimer's disease. Compared to nonsmokers, people who smoked two packs a day in midlife increased their risk of Alzheimer's by 157 percent. Dr. Lancer will talk more about the effects of smoking on the skin in chapter 4. However, suffice it to say that there's such a thing as "smoker's face," characterized by deep lines around the mouth and eyes and a grayish tint to the skin. Nicotine contracts the blood vessels, decreasing blood flow to the skin and all the other major organs in the body.
There are a few other reasons why it's to your advantage to quit smoking. One is that it makes it difficult to exercise at the pace you need to get sizable anti-aging benefits. The other is that smoking can interfere with sleep. To see just how much, researchers at the Johns Hopkins University School of Medicine hooked up 40 smokers and 40 nonsmokers to monitoring machines and looked at their brain waves as they slept. The smokers spent a lot less time in deep sleep, the most rejuvenating kind of slumber, and a lot more time in the lighter stages of sleep, when it's easy to be awakened—possibly in part because they were going through nicotine withdrawal while they slept. The smokers also reported feeling less refreshed in the morning. (You'll learn more about the importance of a good night's sleep in chapter 5.) Smoking is probably the single worst thing you can do to yourself—it's like lying on a train track when you know that the train is coming. Quitting, on the other hand, is perhaps the single best thing you can do for yourself.