PUBLIC HEALTH

Coronary heart disease was almost unknown a hundred years ago. Now it is the commonest cause of death in the world. There is a rising epidemic of diabetes, which causes heart disease, and soon 350 million people will have the disease. Patients are told that they are sick because of the way they live. When they reply that they live like others, who are healthy, they are told their genes are at fault. When they ask which genes, no one knows. When they ask how genes could cause an epidemic, there is no reply. The long and largely fruitless search for the causes of coronary heart disease contrasts sharply with the progress made with its treatment. There is constant pressure on doctors to improve treatment, but little pressure to prevent disease. This is surprising since, while patients are grateful for better treatments, they would prefer not to be ill in the first place. A Chinese physician wrote that inferior doctors treat the sick while mediocre doctors diagnose illness before it becomes apparent; but superior doctors prevent illness!

Across western countries poorer people have the highest rates of heart disease. In the US the disease is most common in historically poorer states such as West Virginia and Kentucky. In the UK it is most common in the industrial towns that grew up during the industrial revolution and in poor rural areas. The maps show that the distribution of deaths from coronary heart disease across England and Wales is remarkably similar to the distribution of infant mortality during the early years of the last century. High infant mortality indicates that babies have a poor environment in the womb and after birth. This link between coronary heart disease and poverty is a paradox. The disease increases rapidly as countries become more affluent so why does it settle among the poor? No aspect of the lifestyles of the poor can explain this. An alternative explanation is that poorer people are more vulnerable to damaging components of a western lifestyle shared by rich and poor alike. New research now suggests that poor people are made vulnerable to heart disease through the adverse conditions they experience in the womb.

In adverse conditions, due to lack of food, stress or other hardships, living things grow more slowly. Babies are no exception. Studies around the world have now shown that people who had low birthweight are at higher risk of heart disease. This is a graded relation. People who weighed 8 pounds are at higher risk than those who weighed 9 pounds: 6-pound babies are at higher risk than 7 pound ones. The people at risk are those who were small at birth because they grew slowly, rather than because they were born prematurely. Low weight gain in the first two years after birth also increases the risk of later heart disease.

Like all living things as they develop babies are plastic and are moulded by the food they receive. This determines how fast they grow and the quality of the systems and structures they develop. During what are called “critical periods” of development undernutrition changes a tissue or system permanently. When the sensitive period is over the effects of undernutrition will have become “hard-wired” in the body, preserved for a lifetime. For most organs and tissues the critical period occurs before birth.

Research is showing why people who had low birthweight are more vulnerable to heart disease, stroke, hypertension, diabetes, osteoporosis and certain cancers. In the womb the heart has to pump blood through the placenta, and in small babies the high pressures in the placenta circulation weaken the heart for life. A baby protects the growth of its brain at the expense of other parts of the body, such as the lung and kidney. Protecting these is not an immediate priority as, until birth, the mother performs many of their functions on the baby’s behalf. These organs are ‘traded off’. We are beginning to understand how ‘trading-off’ can permanently change an organ’s function and lead to disease in later life. The organs of people who had low birthweight have reduced functional capacity. These people also have different hormonal profiles and different metabolism when compared with people who were heavier at birth.

A baby’s growth does not depend only on what its mother eats each day. That would make it too vulnerable to the mother becoming temporarily short of food or ill. It is nourished by its mother’s muscles, fat and bones. Protein, fat and calcium are released from them each day and then re-incorporated back into the tissues. This process, ‘turnover’, constantly enriches the mother’s blood. A woman’s turnover, and her ability to re-fashion food, are built up in response to her dietary experiences through her life. Experience in early life seems to have the greatest impact. Chronic disease is a legacy from malnutrition and poor living conditions among previous generations of girls and young women. The geography of diabetes, heart disease and stroke within any country was laid down by the malnourished mothers of the past. The composition of a good diet was widely agreed many years ago but today the diets of many girls and young women remain unbalanced and monotonous.

Infancy lasts from birth to two years of age. People grow more rapidly during this time than they do at any later age. Almost one quarter of the energy available to an infant is used for growth. The brain remains plastic for some years after birth. Infants who grow slowly tend to achieve less at school and during their working lives and are at increased risk of high blood pressure, heart disease, stroke and diabetes in later life.

The growth of living things does not proceed with all possible speed until some mechanical constraint is reached and they can grow no faster. Rather growth is optimized, limited so that the benefits of larger body size are not outweighed by the nutritional costs of growth. At some age around two years a child’s rate of growth becomes ‘set’ by the internal environment and is less sensitive to the day-to-day supply of food. Until then food has commanded the rate of growth. Now the rate of growth commands the need for food. Excess food will not lead to more growth, but to fatness.

People who develop chronic diseases grow differently as children. A large group of children born in Helsinki, Finland, has been followed up for 65 years. At eleven years of age those who suffered strokes in later life were short and thin; those who developed heart disease were short and of average fatness; while those who developed diabetes were overweight. These children would not have stood out from other children in the class. What distinguished them was the path of growth by which they had attained their body size. This path was characterised by slow growth in the womb and during the first two years after birth followed, in some children, by rapid ‘compensatory’ weight gain. This path of growth leads to a high proportion of fat to muscle in the body, which is known to predispose to heart disease and diabetes. All children should have their growth charted. This is done routinely in some European countries.

The places where life expectancy is longest are those where people are not only healthier but biologically younger. In healthy places seventy-five year old people may be biologically similar to 65 year old people in less healthy places. There are two challenges in later life. One is to avoid age-related diseases, which include heart disease and diabetes: the other is to slow the rate of biological aging. The two challenges are linked but disease is not an inevitable consequence of aging. In later life people who had low birthweight are both at increased risk of disease and are more frail.

Today in the western world mothers should trust nature and enter pregnancy with confidence. They are the custodians of a marvellous system handed down to them through millions of years of evolution. Natural selection has honed the system for success. Growth and survival of the baby is a centrepiece of evolutionary strategy. Most of the process is controlled by nature: the egg’s journey to the womb, the embryo’s implantation, the growth of the placenta, all occur without a mother’s knowledge. The long and complex supply line which brings food from the mother to the baby develops without her consent. She is the arena for nature’s performance but she is the source of food that fuels it. If we protect the health and nutrition of girls and young women we can prevent chronic disease in the next generation. Each year the lives of millions of people will be spared. Many more will be saved from chronic ill health.