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POPSLonliness Impacts Brain Function (continuing on) About one if five Americans experience loneliness, Cacioppo said. And it is a growing problem in modern society in part because the average household size is decreasing. By 2010, 31 million Americans — roughly 10 percent of the population — will live alone, Cacioppo and his colleagues say. Previous work has suggested it can be as detrimental to health as smoking, Cacioppo said. In his book, "Loneliness: Human Nature and the Need for Social Connection" (W.W. Norton, 2008), he presented evidence that loneliness is related to less blood flow through the body, poorer immune systems, increased levels of depression and a faster progression of Alzheimer's disease.