Raised levels of mercury in the blood, from high seafood consumption, are linked to infertility, researchers have found.

The study was carried out in Hong Kong, where people eat a large amount of seafood, and where seas have high levels of pollution.

In the UK, people eat less seafood and there is less pollution.

But UK experts say the Hong Kong findings show the effect environmental pollutants can have on fertility.

People in the UK just don't eat as much seafood

Professor Bill Ledger, Royal Hallamshire Hospital

Mercury is one toxin thought to have an impact on fertility.

Researchers from The Chinese University of Hong Kong studied 150 infertile couples undergoing IVF, and 26 fertile couples.

Blood tests were used to assess the level of mercury in the men and women's system.

A dietician also asked infertile couples about their seafood consumption.

Other potential sources of mercury, such as fish pill supplements or the use of skin-lightening cosmetic creams were also recorded.

Seafood 'only difference'

Overall, the infertile group had significantly higher blood mercury concentrations than the fertile group.

Over a third of infertile men had abnormally high concentrations, as did 23% of infertile women.

The researchers point out that women who are exposed to mercury through their jobs can have irregular periods.

Writing in the British Journal of Obstetrics and Gynaecology, the researchers led by Dr Christine Choy, said: "While comparing infertile subjects having abnormally high blood mercury concentrations, seafood consumption was the only different source of exposure to mercury among various other sources."

They add that contamination of the waters around Hong Kong with heavy metals is common.

A recent study in Thailand which looked at 10 samples of shark's fin found six had concentrations of mercury above the upper safety limit for human consumption.

Tuna and swordfish, which are predatory fish, may also accumulate high concentrations of mercury.

The researchers add: "Reduction in dietary consumption of seafood is a measure that may be effective in controlling the accumulation of mercury.

"However, this should be balanced against the beneficial effects of other components of fish, such as those of 3-omega fatty acids and selenium."

Environmental effects

Bill Ledger, professor of obstetrics and gynaecology at the Royal Hallamshire Hospital, Sheffield, said though the Hong Kong findings did not apply to the UK, there were lessons in terms of the effect of environmental pollutants.

"It's different in Hong Kong, where they eat a huge amount of seafoods and the seas there are highly polluted.

"People in the UK just don't eat as much seafood.

"You would have to have seafood at least three or four times a week."

But he said it did show how environmental pollutants could affect fertility and the impact of long-term exposure.

"For example, working in Sheffield, I see a number of males with low sperm counts because they are working every day with pollutants, such as solvents.

"They are exposed all day every day. People doing some DIY, that's not a problem."