Shift work and physically demanding jobs are linked to lowered fertility among women, according to a new study.
Researchers examined the ovarian reserve, the number of remaining eggs, and the levels of follicle stimulating hormone in 473 women at a fertility clinic.
They found that those who have physically demanding jobs had a lower reserve of eggs than those whose jobs did not regularly require heavy lifting.
Also among women who were going through IVF treatments, those with physically demanding jobs had a lower total reserve of eggs and fewer mature eggs.
The differences were also greater among women who work either evening, night or rotating shift patterns.
These women had fewer mature eggs than those working regular 9-5 hours.
However, these results have already been cautioned on the basis that they are tested from a sample of women who were attending a fertility clinic, and therefore don’t include those who conceive without help.
They were also based on women from one fertility clinic, therefore these results may not apply to women all over the world, and other extraneous factors about the location could also affect the results.
Professor Adam Balen, chairman of the British Fertility Society, said: "In this interesting study, an association has been shown between physically demanding jobs and lower potential fertility."
"It is difficult to hypothesise a mechanism by which a physically demanding job may have a negative effect on ovarian reserve, as the number of eggs (oocytes) is determined at birth and lost progressively throughout life, with smoking having been shown to be the main toxin that significantly diminishes ovarian reserve."
"It is important to note that there was no difference in smoking status between the groups."
"I wonder therefore if there may have been maternal influences on the women studied that could have affected their ovarian reserve at birth, for example maternal smoking and nutrition, which might then have some bearing on the future reproductive health of their daughters."