Boys have up to 10% fewer sperm if their fathers smoked before they were born

Boys have fewer sperm if their fathers smoked cigarettes before they were conceived, a study has found. 

Danish researchers, who presented their conclusion at a major fertility conference, analysed semen samples from almost 800 teenagers.

They discovered those whose fathers smoked daily before they were conceived had sperm concentrations around eight per cent lower.

Experts say the findings ‘add another brick in the wall’ showing the harmful effects of smoking.

Boys have almost 10 per cent less sperm if their fathers smoked cigarettes before they were born, a study in Denmark has found

The dangers of pregnant mothers smoking have long been established, with the NHS warning it can cause low birth weight and disabilities.

However, little is known about whether the father’s smoking status leading up to and during pregnancy affects the unborn child.  

The results were presented at the 35th Annual Meeting of European Society of Human Reproduction and Embryology (ESHRE) in Vienna.

The study was a follow-up analysis of 778 19-year-old young men born to mothers between 1996 and 2002. 

Smoking information, including that on the father, was based on reports from the mother at around gestational week 16. 

Scientists at Bispebjerg Frederiksberg Hospital, Copenhagen, analysed the semen quality of the young men using criteria from the World Health Organization.

This meant they compared sperm concentration, total sperm count, morphology and sperm motility.

Sons of fathers who smoked daily, and where the mothers did not smoke, had an eight per cent lower sperm concentration.

Their total sperm count was also nine per cent lower than the sons of non-smoking fathers, the results showed. 

Investigator Dr Sandra Søgaard Tøttenborg said this can seriously affect the fertility of men with already sub-optimal sperm quality.

The drop in sperm count is in the same range as that associated with smoking in the adult man, she said. 

However, Dr Tøttenborg concluded the effect of maternal smoking on sperm quality is much larger than paternal.

‘If the mother but not the father smoked, the reduction was 26 per cent for sperm concentration and 46 per cent for sperm count,’ she said.

‘Nevertheless, the circumstances in which the father smokes but the mother doesn’t is much more prevalent, so this is still very relevant for public health.’

Other studies have delved into how paternal smoking destroys semen quality, but they have been much smaller samples.  

Paternal smoking is thought to cause alterations in the man’s sperm genome, which in turn may be transmitted to the cells of the child.

Professor Richard Sharpe, of the University of Edinburgh and member of the Society for Endocrinology, said the study does not find a ’cause and effect’.

However, he added: ‘The consistency of the findings for maternal smoking in now five independent studies makes it more likely that this is cause and effect.’

Professor Sharpe suggested exposure to chemicals in tobacco smoke may slash the number of sertoli cells – considered vital for producing sperm.

Allan Pacey, professor of andrology at University of Sheffield, said: ‘I do wonder if it simply a case of “passive smoking” by the mother.’

He said ‘presumably’ the fathers and mothers of the teenage males involved in the study shared a common household.

Professor Pacey said: ‘However, regardless of the precise biological effect, the data does serve to illustrate the need for both future fathers and mothers to be as healthy as possible, both before and during a pregnancy.’

Smoking during pregnancy, as well as drinking alcohol, has many health consequences. It raises the risk of miscarriage or premature birth and can lead to disability in children.

The NHS states that passive smoke can affect the pregnant women and the baby both before and after birth.

Second-hand smoke can also reduce the baby’s birth-weight and increase the risk of cot death.

Babies whose parents smoke are more likely to be admitted to hospital for bronchitis and pneumonia during their first year.


Cigarettes can restrict the essential oxygen supply to the baby. As a result, their heart has to beat harder every time the mother smokes

Dangers include: 

Increased risk of complications in pregnancy and birth

Less likely to have a healthier pregnancy and a healthier baby

Increased risk of stillbirth

Baby more likely to be born too early and have to face the additional breathing, feeding and health problems that often go with being premature.  

Baby more likely to be born underweight: babies of women who smoke are, on average about 8oz lighter than other babies. This means they’re more likely to struggle keeping warm and are more prone to infection

Increased risk of cot death

Each year, smoking during pregnancy in the UK causes an estimated:

2,200 premature births

5,000 miscarriages

300 stillbirths 

Source: NHS