In a recent online post, Vidya Yeravdekar, chancellor of Symbiosis University, noted that the jamun fruit (Indian blackberry) started falling from trees earlier this year. She recalled her grandmother’s comment from years ago that an early fall of the jamun portends a period of diminished rainfall and possibly a drought. This is not mere folklore. It is indeed a recorded scientific observation. The phenomenon is called ‘drought escape’ or ‘stress fruiting’. In conditions of water shortage, plants like jamun yield smaller fruits with higher sugar content.
Tacit knowledge of communities stored as experiential wisdom reflects past observations. It is of value even if it is not an accurate meteorological forecasting based on modern scientific methods. The anecdote is a timely reminder that nature retains a long memory and uses its recall to fashion a species survival response in the plant. When its roots are alerted by unfavourable environmental signals related to soil moisture, the plant prioritises flowers and fruit over new branches and leaves. Anthropogenic climate change is now stretching the limits of nature’s ingenuity.
A similar phenomenon is also observed in human beings. When a growing foetus or young infant suffers early childhood malnutrition, there is early sexual maturation. This is especially evident among females. Early menarche (onset of menstruation) can be accompanied by increased fertility if there is improved nutrition as the child grows. If social customs force an early marriage, a spate of teenage pregnancies can result.
Even more alarming is the widespread impact of sequential early childhood malnutrition followed by an adiposity rebound in later childhood and adolescence. Physiological programming, of the epigenetic levers of gene expression, results in a ‘metabolic mismatch’ of the nutritional parsimony experienced in the early years of life and relative caloric largesse in later life.
British epidemiologist David Barker drew attention to the ‘foetal origins of adult heart disease’ by initially pointing out that the high rates of premature adult deaths from coronary heart disease in England and Wales correlated with high infant mortality rates of earlier decades (reflecting adverse early childhood influences). He later showed the association of low birth weight and small birth size with early onset of coronary heart disease in adult life. Many studies across the world corroborated this association.
In India too, studies in Delhi, Mysuru, Vellore and Pune have affirmed the link between early childhood malnutrition and adult cardio-metabolic diseases—diabetes, hypertension and coronary heart disease.
A team of University of Auckland scientists led by Peter Gluckman showed that these effects are not due to structural alterations in genes but are mediated by functional changes in gene expression. Such ‘epigenetic’ modifications up-regulate or down-regulate gene functions. These can extend across several generations but are also potentially modifiable within an individual’s lifetime under the influence of behavioural and socio-environmental factors.
The heightened risk of cardio-metabolic diseases in adulthood results from mechanisms that nature crafted to ensure the survival of the undernourished foetus, infant and young child. Muscle mass is kept lean and the muscle membrane becomes resistant to the action of insulin. This is because glucose should be prioritised for use by the brain and nervous system and not be burnt up by the muscle. Being more essential for survival, the brain wins nature’s vote against the muscles. Most of the other organs assume a modest size to let the brain become the maestro.
Among the blood cholesterol sub-fractions, high-density lipoprotein (HDL) levels are reduced and low-density lipoprotein (LDL) levels are increased. This ensures that cholesterol is deposited in the brain and blood vessels rather than being drawn away from them. Underutilised blood sugar also gets converted to triglycerides. Abdominal fat deposits increase, to store energy for hard times.
Sugar which is kept out of the muscle cells gets converted to triglycerides. Inflammatory responses to perceived or potential threats are heightened. Platelet activation and coagulation pathways too are easily triggered to prevent life threatening bleeding. Malnourished babies have higher levels of fibrinogen and coagulation factor VII.
When these imprinted changes of gene expression in the ‘thrifty phenotype’ operate during the rest of the life course, diabetes and cardiovascular disease become more likely. Abdominal obesity becomes a prominent feature. Inflammation strikes blood vessels and many other body tissues. The protective armour of the foetus and infant becomes a straitjacket for the adult.
These epigenetic mechanisms need not be permanently switched on in the same mode. Physical activity reduces insulin resistance. As insulin- sensitive muscle membranes permit more sugar to enter exercising muscles to be ‘burnt up’, risk of diabetes is decreased. A diet which is rich in fibre from fruit and vegetables enables the growth of a healthy gut ‘microbiome’. Such a collection of friendly bacteria produces short-chain fatty acids which are anti-inflammatory.
Ricardo Uauy, a paediatrician in Chile, first showed that supplemental nutrition to low birthweight children runs the risk of making them stunted and obese due to the programming mismatch. The answer lies in ensuring balanced fibre- and protein-rich diets with low levels of refined carbohydrates, coupled with high levels of physical activity to overcome insulin resistance. We must ensure that low birth-weight children can grow to their physical and intellectual potential, without becoming victims of obesity, diabetes and heart disease. This is the lesson for India, as we are now confronted with both undernutrition and obesity in childhood.
Unfortunately, many Indians display the combination of abdominal obesity, reduced skeletal muscle mass, insulin resistance, low HDL cholesterol and increases in LDL and triglyceride levels in the blood. Smoking, air pollution and psychological stress also produce similar changes in the body. While the unfavourable physiological profile is epigenetically directed towards an excess risk of cardio-metabolic disease, the problem is further compounded by flawed human behaviours.
Nature is the most elegant designer of complex but smoothly interacting physiological systems, and is also the most astute planner of crisis-coping strategies. Nature never failed in its mission to sustain life during adversity—till humans foiled it.
K Srinath Reddy | Chancellor, PHFI University of Public Health Sciences; and Chair, Centre for Universal Health Assurance, Indian School of Public Policy
(Views are personal)
(ksrinath.reddy@phfi.org)