care: 10 percent
The relative weighting of these categories is likely to change as our knowledge of human genetics and biology increases and as we can translate this knowledge into more effective approaches to prediction and prevention. As discussed in the vignette at the beginning of the introduction, more‐precise tests that screen for risk factors and enable diagnosis of disease at a much earlier stage are on the way. Although the specific percentages for each area vary among studies [1], the categories are not isolated—they clearly interact with each other. We know, for example, that the environment in which a person lives can have a profound influence on individual behavior. In the United States, for example, obesity [2] and the use of tobacco [3] tend to be more concentrated among people with low incomes. But the universal conclusion from all studies that have addressed this topic is that social, environmental, and behavioral factors are highly significant determinants of health. Recently, Robert M. Kaplan and Arnold Milstein, both of Stanford, reviewed the contributions of medical care to health outcomes, drawing on the conclusions reached in four major studies. They stated, “Healthcare has modest effects on the extension of U.S. life expectancy, while behavioral and social determinants may have larger effects” [4].
There are many reasons why behavioral and social determinants have received far less attention, particularly in the community of academic medicine, compared with genetics and medical care. These reasons include cultural expectations (physicians being identified with the treatment rather than the prevention of disease), perverse incentives in payment systems (reimbursements for care delivered and procedures performed that are not necessarily linked to outcomes), and the sheer complexity of these factors. The net effect has been a relative paucity of studies and actionable changes in social, environmental, and behavioral determinants.
But the future, as I will describe in the pages that follow, offers tremendous opportunities to transform health by moving from reactive medical care to proactive health care. We are living amid a biomedical revolution. Our understanding of the mechanisms of disease is growing in ways that enable us to prevent diseases altogether or diagnose them, and therefore treat them, much earlier and more effectively. New technologies applied to the monitoring of health will play an important role. Finally, the engagement of each of us in our health and well‐being, enabled by the information we have about our health, can be transformative.
PRECISION HEALTH AND POPULATION HEALTH
This chapter highlights some population‐level health challenges, such as obesity and poor nutrition. The wide‐ranging remedies that are typically utilized to help meet such broad challenges contrast with the Precision Health approaches, which are tailored to specific individuals. But the two are not in conflict. In fact, they can complement each other, thanks to the explosion of data generated from sources such as wearable devices, electronic health records, insurance claims, and clinical trials. These data, when coupled with the technology to manage and analyze them, make it possible to target emerging diseases with precise interventions at the level of the individual and at the level of the population as a whole. For example, as we further explore the roles of diet and exercise in preventing cardiovascular disease and cancer, we are likely to discover optimal combinations of certain behaviors for certain genotypes and phenotypes, leading to precise approaches to prevention rather than the one‐size‐fits‐all public guidance that has long characterized our approach.
The intersection of population health and Precision Health has also enabled the creation of new scientific approaches to meet health challenges. That was part of the impetus for Stanford establishing the Center for Population Health Sciences in 2015. The center is focused on improving individual and population health by fostering collaboration across diverse disciplines and data, with the goal of understanding and addressing social, environmental, behavioral, and biological factors on a domestic and global scale. It has more than 750 members, more than 230 research trainees, 42 community partners, and research in 24 countries. Its research initiatives span a wide variety of topics, including community resilience and socioeconomic equity, gender, and healthy aging. The center’s work emphasizes linking the precise determinants of an individual’s health to the underlying drivers of population health—encompassing lifestyle choices, social factors, the environment, infectious agents, medical care, and genetics.
By applying Precision Health solutions to improve population health, especially in underserved populations, and by using lessons learned from large populations to predict, prevent, and cure more precisely, we can maximize wellness for all individuals and impact millions of lives.
GENES ARE ONE PIECE OF THE HEALTH PUZZLE
The belief that genetics is the overwhelmingly dominant determinant of health is, in many respects, unfortunate. This is not to say that genetic determinants of disease are unimportant—quite to the contrary. But it is also incorrect for people to believe they are at the mercy of their genes and medical care, and thus their individual behaviors don’t have significant impact. The reality is dramatically different. As Cashell Jaquish, a genetic epidemiologist at the National Heart, Lung, and Blood Institute, has said, even a genetic predisposition to heart disease (the leading cause of death among Americans) “doesn’t mean you are fated to have [it]. Other factors, like not smoking, diet and exercise, can have a very large effect. Family history does increase your risk slightly, but not as much as [not doing] these other things” [5].
The nexus between genes and many chronic conditions can also be overcome with smart behavioral patterns. Consider obesity. “I like to say that obesity is 80 percent genetic and 100 percent environmental,” Philip F. Smith, codirector of the office of obesity research at the National Institute of Diabetes and Digestive and Kidney Diseases, told the Washington Post. “You won’t become obese unless you overeat.” He added, “For most people, I can say unequivocally that genes are not your destiny. They can predispose you to obesity, but only if you consume more calories than you burn off” [6].
Further proof of that comes from a 2007 study, published in the New England Journal of Medicine, based on people who were part of the landmark Framingham Heart Study. Although the study found that obesity was 40 percent more likely if one’s sibling had already become obese, it was 57 percent more likely if someone’s friend had become obese, and 171 percent more likely among close mutual friends [7]. One of the study’s coauthors pointed out, “What appears to be happening is that a person becoming obese most likely causes a change of norms about what counts as an appropriate body size. People come to think that it is okay to be bigger since those around them are bigger, and this sensibility spreads” [8]. A related issue is that close friends eat together and end up taking cues from each other about what’s customary when it comes to the types of foods to eat and how much.
Physical activity can help neutralize the impact of a genetic predisposition to obesity. A study published in 2011, involving more than 200,000 adults, found that although a certain gene variant (FTO) increased the risk of obesity by 23 percent, those with the variant who were physically active had a risk of obesity 27 percent lower than that of inactive adults [9].
While genes are not the exclusive drivers of health, the environment in which one lives—both the social and physical dimensions—is a critical influence. That influence takes several different forms, but it starts with something basic: social connections. “People who feel more connected to others have lower levels of anxiety and depression,” says Emma Seppälä, science director of the Stanford Center for Compassion and Altruism Research and Education and the author of The Happiness Track: How to Apply the Science of Happiness to Accelerate Your Success. She also points to studies showing that connected people have higher self‐esteem and greater empathy for others. They are also more trusting and cooperative, and as a consequence, she says, “others are more open to trusting and cooperating with them. … In other words, social connectedness generates a positive feedback loop of social, emotional and physical well‐being.”
A few years ago, trained interviewers met with 100 people from Santa Clara County (the county that encompasses most of Stanford) as part of a project launched by the Stanford Prevention Research Center. The questions during