Fresh evidence smoking damages fertility

Two new studies have
revealed further evidence of the harmful effect of smoking on both male and
female fertility. The first study found
that prenatal exposure to maternal cigarette smoke reduces the number of
germ cells and somatic cells in human embryonic
testicles and ovaries.

Embryonic germ cells
eventually form sperm in men and eggs in women, meaning a mother's smoking
could influence the future fertility of her children. Equally, a reduction in
the number of somatic cells in the testes could affect development of germ
cells and functional sperm.

Although smoking during
pregnancy has become less popular in industrialised countries during the last
decade, one in eight mothers continues to smoke during their pregnancy.

Claus Yding Andersen,
Professor of Human Reproductive Physiology at the University Hospital of
Copenhagen (Denmark), and his colleagues studied 24 testes from
embryos terminated between 37 and 68 days after conception. The embryos were taken
from women aged 19-39 years whose smoking habits were monitored through
questionnaires and urine samples. The researchers combined this work with past
studies on 28 female embryos.

The number of germ cells was 55 per cent lower among male embryos from
mothers who smoked compared to non-exposed embryos. Mothers' smoking also
lowered the number of somatic cells in the embryos' testicles
or ovaries. The effects were dose
dependent with greater damage to germ and somatic cells found in embryos from
the mothers who smoked the most.

These findings may potentially
explain reduced fertility but the study, according to its authors: 'does not
clarify whether the reduction in cell numbers (i.e. somatic and germ cells) is
permanent or reflects a growth delay, which may be compensated for later in
life'.

The second study, led by
Professor Mohamed Hammadeh, Head of the Assisted Reproductive Laboratory in the
Department of Obstetrics and Gynaecology at Saarland University (Germany),
looked at the levels of two proteins believed essential for healthy sperm
formation in the sperm of 53 heavy smokers (more than 20 a day) and 63
non-smokers. Deficiencies of the two proteins
- protamines P1 and P2 - can led to infertility. Concentrations of P2 in
the sperm of smokers was significantly lower than in non-smokers, leading to an
abnormal P1/P2 ratio.

'In normal, fertile men,
the ratio of P1 to P2 is almost equal at 1:1. Any increase or decrease in this
ratio represents some kind of infertility', said Professor Hammadeh.

Both studies were published in the online
journal Human Reproduction.