What is the most common risk factor for serious disease?

The most common risk factor for serious disease is old age. Heart disease, cancer, stroke, neurological conditions, diabetes — all increase radically with advancing years. And the older a person is, the more likely he or she is to have multiple chronic illnesses.
   Some scientists hope one day to treat all of them at once — by targeting aging itself.
   Humans aren’t built to last forever. The oldest person on record was Jeanne Calment, a Frenchwoman, who died in 1997 at the age of 122. In 2040, the average life span for people in Spain, projected to pass Japan as the country with the longest-lived citizens, will reach about 86 years.
   There is considerable dispute, however, over how long humans might live under optimal circumstances. In 2016, a team of scientists declared the upper limit to be 115 years. But in June, researchers reviewing death rates among elderly Italians suggested that there may be no limit at all.
   In animal studies over the last few decades, scientists have begun to understand the specific cellular and molecular processes that cause the deteriorations of old age.
   Old cells, researchers have found, secrete proteins, lipids and other substances that increase inflammation and tissue destruction. In one study in mice, researchers showed that transplanting these cells to the knee joints of healthy animals causes disease that looks very much like human osteoarthritis.
   Healthy young people have few of these aging cells, but after age 60, they begin to accumulate, and their increasing quantity correlates with disabilities of old age.
   Could there be any remedy that removes these old cells while leaving young cells? Several are being tested.
   Some drugs already approved for other purposes are being tested as "senolytics", as the drugs that kill old cells are now called.
   Dr. Nir Barzilai, a professor of medicine at the Albert Einstein School of Medicine, is planning a study of metformin, a drug that has been used for 60 years to treat diabetes and has been shown to be effective against several age-related diseases.
   If drugs can treat aging, is aging itself a disease? No, Dr. Barzilai said.
   "Neither I nor the Food and Drug Administration is interested in calling aging a disease. Our study is to show that we can prevent a composite of age-related diseases — cardiovascular, cancer, cognitive — and ultimately affect mortality. "
   But we will all die. No serious scientist believes in immortality. But we also are closer to assuring healthier old age than ever before.