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From placenta to play centre

How much do we know about when disease starts

The importance of the early childhood years in shaping adult life is not a new concept. For many years now, parents have been playing, talking, reading, singing, and exercising their children in increasingly more refined ways in the (quite correct) belief that these behaviours will lead to better and happier outcomes.

However, there is a growing body of evidence that our ability to promote the healthiest outcomes for children starts well before birth.

Barker hypothesis

Over the past 25 years, there has been a revolution in the way that the scientific world perceives the origins of many diseases of adult life. The Developmental Origins of Health and Disease (DOHaD) concept emerged from observations of Professor David Barker and colleagues, who found that children with low birth weight were at increased risk of developing heart diseases and type II diabetes later in life.

The Barker hypothesis was that pregnant women “programme” the developing fetus for the metabolic world in which she (and presumably her offspring) will be living. In those instances where nutrient flow is disrupted, the fetus is biologically programmed to expect a life of “thrift”.

If this offspring then encounters a world of “plenty”, such as the modern Westernized world, this mismatch will result in susceptibility to a range of cardiovascular and metabolic diseases.

Subsequent epidemiological and experimental research has linked reduced size at birth to a host of chronic adult diseases, including osteoporosis, polycystic ovarian syndrome and obesity.

Although fetal nutrition has received the most research in the DOHaD field, other environmental factors during prenatal life have also been investigated.

Season of birth

Among the most interesting associations observed are those between season of birth and a range of neurodevelopmental disorders. Schizophrenia, for example, is known to be more common among adults born during the winter and spring months. This small but significant effect - around a 7% increase in risk - is thought to reflect differential exposure seasonal factors that may influence fetal neurodevelopment, such as changes in temperature, as well as maternal nutrition, sunlight exposure and risk of infection.

Similar “season of birth/conception” effects have been observed for multiple sclerosis, autism and language impairment, albeit at varying times of year.

Fathers have also come under investigation in the DOHaD arena, through the study of epigenetics. Epigenetics refers to changes in gene function that do not involve changes to the genetic code but still get passed down to offspring. One study of historical records in Northern Sweden found that men were more likely to die from cardiovascular disease if their paternal grandfather was exposed to abundant nutrition during childhood (based on regional harvest statistics).

A further study found that fathers who smoked during mid-childhood had sons with a greater body mass index. These findings, combined with a great deal of animal research, suggest that environmental exposures can have inter-generational effects that are passed down the male line.

One of the challenges for the field is how translate newfound knowledge into public awareness without unnecessarily alarming prospective parents. This website has previously published on this issue.

We now have a clear indication that several environmental toxins, such as tobacco, alcohol and illicit drugs, can be harmful to offspring health and should be avoided. But the mechanisms underlying other factors, such as the season of conception/birth, are still far from conclusive, making it premature to submit any recommendations to parents about timing the conception, pregnancy or birth of their child around specific seasons.

A final word of caution: the very idea of the developmental origins of health and disease is very attractive to media, and it’s not uncommon to read reports about over/underweight mums/dads “causing” [enter disease of choice here].

I urge readers to view these reports with a “critical eye”, appraising the science behind the stories before making their own conclusion.

The DOHaD field is now well into its third decade. Increasingly, larger and more detailed inter-generational data sets are becoming available, enabling even greater insights into how early life (and even pre-life!) experiences can affect adult health. Enjoy the excitement of this field - I am!
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