"One possibility is that the population they looked at is not a representative population," Kelly said. Previous studies have shown that older men with higher levels of testosterone scored better on tests of executive function and attention, he said.

It's also possible that the tests used in the study "were not broad enough to assess all the changes in cognitive function," Kelly said.

Both Kelly and Snider also noted that the findings were based on blood tests alone. "They're looking in the blood, but what matters is the level in the brain," Snider said. According to Kelly, the relationship between blood levels and brain levels of the hormones remains "an unanswered question."

"We don't understand how these hormones interact with Alzheimer's disease," Snider said. "Hopefully what this study will do is spur studies to look at the role of estrogen in men."

Poison warning over apricot seeds

  Apricot seeds which are sold for their health benefits could be poisonous if eaten in large quantities, the Food Standards Agency said today.

They can produce cyanide and could be fatal in high doses over a short period of time, the Government's food watchdog warned.

A maximum of two bitter apricot kernels may be safely eaten in one day, it said.

Natural food retailer Julian Graves pulled the seeds from shop shelves after it was found selling packs with a recommended daily dosage of up to 10 kernels.

Bitter apricot kernels are thought to contain high levels of vitamin B17, known as laetrile, which has been described as an immune system-booster and even as a cancer treatment.

Julian Graves - which has 280 UK outlets - said in January that it was the country's first high street retailer to stock the "controversial" product.

The seeds are also available in the UK via specialist websites.

But Cancer Research UK's website reference to B17 says: "According to claims made on the Internet, this substance found in apricot pips is a highly active compound that can cure cancer.

"Unfortunately this is simply not true. The whole reason for the existence of Cancer Research UK is to find cures for cancers. If simply eating apricot seeds could cure cancer, no one would be more delighted than us."

The FSA's warning follows the advice of its Committee on Toxicity regarding bitter apricot kernels.

A spokesman for the food watchdog said the kernels were a niche product in the UK, but added: "There have been reports from overseas of consumption of 20 to 30 kernels by adults in a short period of time being associated with very serious health effects. They could potentially be lethal in high enough doses."

Julian Graves spokeswoman Stephanie Goodman said the chain had started selling bitter apricot kernels due to high customer demand.

"We advise people to do their own research and make their own minds up. We really don't go into the reasons why people are buying them because there have been absolutely no trials done on this product," she said.

The chain pulled them in line with FSA advice but would start selling them again with a revised dosage recommendation if the food watchdog gave it permission to do so, she added.

Other shops and websites may still be selling the kernels without accompanying advice about the correct maximum dosage, the FSA warned.

The watchdog will discuss possible EU action to protect consumers at a meeting with the European Commission and other member states on April 21.