In 2004 the world had just mapped the human genome for the first time. They knew the genome would only explain a small part of the health and the ageing of the population. The environment in all its forms would account for far more individual differences. The EXPOSOME was conceived to fill the gap.
The impact of the environment is demonstrated in a study in Sweden, Denmark and Finland. There researchers had assembled over 44,000 sets of twins. They studied the incidence of many different cancers. If one twin got cancer, what were the odds the other would get it, compared to the odds for the general population? They were able to measure how much the different cancers were inherited. Some cancers such as breast and prostate cancer were hereditary. At least 25% and 45% was inherited respectively. Others were not. They looked across twenty eight cancers. Their overall conclusion was that:
“inherited genetic factors make a minor contribution to susceptibility to most types of cancer. The environment has the principal role in causing sporadic cancer”.
It is generally thought that 80% of health and ageing is due to the environment.
Defining the EXPOSOME
“The cumulative measure of environmental influence and associated biological responses throughout the lifespan including pressures from environment, diet, behaviour and endogenous processes”
Every word has been carefully chosen. The effects are deemed to be cumulative. A particular food can have a detrimental effect in the short run. Later in life it can have another impact. It can even act in combination with a different pressure. The effects are additive. The environment affects us throughout our lives.
I recently attended a Conference run by UK National Innovation Centre for Ageing. Dr Paul Shiels is Professor of Geroscience at the University of Glasgow. He gave a lecture on the Exposome. He was motivated by the low life expectancy and poor health of Glasgow. In particular the two boroughs that perform worse than the rest. (These parts of Glasgow rank lowest in the UK on life expectancy). As an example of the impact of diet he quoted meat eating. Humans are omnivores. In the parts of Glasgow with the lowest life expectancy people eat excess meat. (All be it in highly processed forms such as bacon and sausages). He looked for analogous carnivores in nature. The diseases plaguing those particular Glaswegians were also common in the top carnivore. They had the same diseases as lions.
Prof Shiels also works on the positive side of food. Food can be a medicine. He argues that ageing is in part caused by low levels of background inflammation. Researchers are looking for drug based solutions. Instead he believes that our diets can influence that inflammation. He postulates that our food can influence our health through the gut microbiome.
We respond to environmental pressures biologically throughout our lives. For example, we may produce enzymes under stress. These in turn may have a negative impact on our health now or in the future. Those stresses can come from many parts of the environment. In London asthma is more common close to concentrations of air pollution. It is not only the macro-environment. Our homes can be an issue. Prof Shiels mentioned studies of the number of people with whom you shared your bedroom as a child. This will affect the strength of your lungs for the rest of your life.
Our social relationships can have as big an impact as the physical environment. Our family and our community can influence our future health. Those effects can also occur early in life and last until death.
We seem to be at our most susceptible when young. Researchers have developed scales to measure Adverse Childhood Experiences or ACE’s . (You can test your own ACE’s on the Harvard Test). They relate the scores of tests like these to health in later life. Stress in childhood is a predictor of disease later. With high ACE's coronary disease, cancer, diabetes and even skeletal fractures are all more common.
The ACE measures include all stressors within the household. Psychological, physical or sexual abuse of you as a child. Violence against your mother. Living in the household with substance abusers, or the mentally ill or suicidal. They even look at the presence of criminals. Some tests include lesser stressors such as divorces. (See the Harvard Test). There are other social stressors outside the household that can affect a child. Such things include racism and violence. There are also protective factors inside and outside the home. Most of them are supportive relationships. The impact is also influenced by the genome. This will influence the underlying resilience of an individual. There is a two way relationship between Genome and Exposome. Endogenous factors are included in the Exposome. These include internal changes in the microbiome and cell activity.
The complexity of the relationships within the Exposome is shown by those studying childhood stressors. The effect is cumulative, with biological and psychological responses both involved. A stressful childhood leads to social, emotional and cognitive impairments. These in turn lead to the adoption of health risk behaviours. It is those behaviours that result in chronic diseases and death. The list of health risk behaviours that have been related to ACE’s is huge. Consider individuals who have experienced four or more ACE’s. They are anywhere between four and twelve times more likely to abuse alcohol and drugs. They are as equally likely to suffer depression and to attempt suicide. They are between two and four times more likely to smoke and have many sexual partners. They are fifty percent more likely to be sedentary and become severely obese.
Living to a healthy old age starts in childhood. Indeed it starts pre-conception with the health of the mother.