Father’s role beyond fertilisation

Traditionally, women are held largely accountable for their offspring’s health. The male sperm is no doubt necessary for fertilisation but seems less important for the subsequent development compared to the female egg.

However, growing research now suggests that the father’s role extends well beyond providing his half of the genetic information. It is capable of influencing embryo quality and offspring health for as many as four generations!

The powerful epigenetics

We all know that half of our genetics comes from the mother, and the other half comes from the father. But that’s not all we get from parents.

Epigenetics carry information beyond the static DNA sequences. It is not about the genetic code, but how the DNA sequence is used. Epigenetic information, unlike DNA, are highly dynamic and influenced by the environment. Mounting evidence now suggests that parents’ environmental exposures and lifestyle can affect both the embryo development and the health of future generations.

Paternal contributions to epigenetic inheritance was largely considered unlikely in the past, as the size of sperm is much smaller than the egg. However, researchers have found that despite its small size, sperm brings along various epigenetic masks on the DNA, regulatory proteins, and RNAs. These findings suggest successful reproduction no longer relies on sperm’s genetic quality only, but also its epigenetic quality.

Harmful environmental and lifestyle factors

Evidence from animal models and epidemiological data have suggested several environmental toxins that can lead to epigenetic inheritance, including:

  • Quantity and quality of diet
  • Alcohol
  • Persistent organic pollutants, eg. Pesticides, DDT, carbon tetrachloride
  • Cigarettes and nicotine
  • Cocaine
  • Obesity
  • Psychological stress

Notably, most women are encouraged to improve their nutrition and use supplements when conceiving or pregnant. Prospective fathers are rarely told that their diet matters too.

For example, folate is a well-known pregnancy nutrient that is supplemented by mothers to prevent neural tube defects. However, a study showed that folate deficiency in male mice also contributed to increased birth defects in the offspring.

Persistent organic pollutants such as DDT could perturb sperm’s epigenetic information across multiple generations in rats, and folic acid supplementation partly reduced the damage.

When researchers fed male mice with unbalanced diets, such as a low protein diet, high fat diet, or folate-deficient diet, detrimental epigenetic changes were detected. These led to metabolic disorders in the offspring, including problems with glucose-insulin and cholesterol metabolism.

In humans, both paternal obesity and malnutrition have been associated with chronic diseases and metabolic disorders in the offspring. Studies on three generations of males showed a correlation between food availability to grandfathers and health and mortality rates in their grandchildren.

While more human research is needed to establish more specific long-term health effects of paternal epigenetics, existing evidence from animal models suggest increased risks of obesity, metabolic disorders, behavioural disorders, and disrobed offspring development.

What about IVF babies?

A few studies reported that the effects of paternal exposure, such as diet and stress, have similar effects on IVF babies compared to those naturally conceived. This has implications for couples using donor sperm, as the sperm donor’s lifestyle becomes a determinant of the health of babies conceived through donor IVF.

Bottom line

The takeaway message here is that having a baby is a fair teamwork. The father’s lifestyle and environmental exposures are equally important as the mother. When planning a pregnancy, both partners can have far-reaching impact on their offspring’s health.