Makes children either badly behaved or low achievers at school

CAN having more children slow the ageing process in women and make children either badly behaved or low achievers at school?

Two new but independent studies suggest the more children a mother has, the slower she may age, and that the size of a family really can affect the behaviour and achievements of children.

Researchers, in a study published in journal PLOS One, reveal that women who had more children had longer telomeres than women who had fewer children.

Previously, animal studies had supported the “life history theory,” suggesting that higher reproductive behaviour is associated with accelerated biological ageing.

However, this latest study, led by Prof. Pablo Nepomnaschy and Cindy Barha – both of Simon Fraser University in Canada – contradicts this theory.

The team enrolled 75 Kaqchikel Mayan women from two neighbouring communities in the south-west highlands of Guatemala, assessing how many children the women gave birth to between 2000-2013.

At the beginning of the 13-year study period, the women’s telomere length was measured from saliva samples. Telomere length was measured again at study end, but through a buccal swab.

Telomeres are caps at the end of each Deoxy ribo-Nucleic Acid (DNA)/genetic material strand that protect our chromosomes – thread-like structures that contain all our genetic information – from damage.

Each time a cell replicates, telomeres become shorter. They eventually become so short that they stop protecting chromosomes, leaving them vulnerable to damage, which in turn causes our cells to age and stop functioning effectively.

The researchers found that women who had a higher number of surviving offspring over the course of 13 years had longer telomeres than those who gave birth to fewer surviving children; each additional child born was linked to 0.059 more telomere units.

These results remained after accounting for potential influential factors, including women’s age, their age at first birth, their age in 2013, lifestyle habits and family income.

Also, scientists believe the size of a family really can affect the behaviour and achievements of children.

A new study has found that for every additional child born, the others are more likely to suffer poor cognitive abilities and behavioural problems afterwards.

Boys were more likely to misbehave while girls saw their performance in mathematics and reading skills dip.

Using data from 1986 to 2012 taken by the National Longitudinal Survey of Youth (NLSY) and by the Children and Young Adult Survey, three economists analysed how older siblings performed before and after a younger sibling was born.

They looked at the number and timing of births into a family and matched these to various mental and behavioural traits.

Levels of parental engagement were also crucial – with factors like how often families eat meals together, one-on-one time with each child, affection and the safety of the home also affecting how a child performed.

As families got bigger, the time spent with each child reduced, which has been linked to worse outcomes for children, they found.

The research paper noted: “Our fixed effect estimates indicate that the arrival of a younger sibling reduces measures of parental investment as well as cognitive and non-cognitive outcomes of older children by approximately one-tenth of a standard deviation.”

The study was conducted by economists Chinhui Juhn, Yona Rubinstein, and C. Andrew Zuppann, who questioned whether the ‘quantity’ of children would effect the ‘quality’ of their upbringing.

It discovered that parental investment in older kids fell by three percentile points after a young child is born, while cognitive scores fell by 2.8 percentile points and behavioural problems increased.

“On average, children in larger families have lowered parental investment and worse cognitive and non-cognitive outcomes.”

Other factors found to influence the outcomes was the mother’s intelligence and economic well-being.

Mothers were asked to take the Armed Force Qualification Test (AFQT), used by the military to assess skills including reading and reasoning.

Those who scored badly saw a larger drop in cognitive scores when they had their second child.

The study follows another by German researchers, which found the first-born in a family tends to be the smartest – and each successive sibling is slightly less bright.

The Leipzig University researchers were unsure why big brothers and sisters seemed to be the most blessed – but suggested it could be because they benefit from their parents’ undivided attention – at least until a little brother or sister comes along.