The researchers found evidence that fungi can “lock” depleted uranium into a mineral form that may be less likely to find its way into plants, animals, or the water supply.

“This work provides yet another example of the incredible properties of microorganisms in effecting transformations of metals and minerals in the natural environment,” said Geoffrey Gadd of the University of Dundee in Scotland. “Because fungi are perfectly suited as biogeochemical agents, often dominate the biota in polluted soils, and play a major role in the establishment and survival of plants through their association with roots, fungal-based approaches should not be neglected in remediation attempts for metal-polluted soils.”

The testing of depleted-uranium ammunition and its recent use in Iraq and the Balkans has led to contamination of the environment with the unstable metal, Gadd explained. Depleted uranium differs from natural uranium in the balance of isotopes it contains. It is the byproduct of uranium enrichment for use in nuclear reactors or nuclear weapons and is valued for its very high density. Although less radioactive than natural uranium, depleted uranium is just as toxic and poses a threat to people.

In the new study, the researchers found that free-living and plant symbiotic (mycorrhizal) fungi can colonize depleted-uranium surfaces and transform the metal into uranyl phosphate minerals.

While they probably still pose some threat, he said, “The fungal-produced minerals are capable of long-term uranium retention, so this may help prevent uptake of uranium by plants, animals, and microbes. It might also prevent the spent uranium from leaching out from the soil.”

Gadd said that a combination of environmental and biological factors is involved in the process. First, the unstable uranium metal gets coated with a layer of oxides. Moisture in the environment also “corrodes” the depleted uranium, encouraging fungal colonization and growth. While the fungi grow, they produce acidic substances, which corrode the depleted uranium even further. Some of the substances produced include organic acids that convert the uranium into a form that the fungi can take up or that can interact with other compounds. Ultimately, he said, the interaction of soluble forms of uranium with phosphate leads to the formation of the new uranium minerals that get deposited around the fungal biomass.

“We have shown for the first time that fungi can transform metallic uranium into minerals, which are capable of long-term uranium retention,” the researchers concluded. “This phenomenon could be relevant to the future development of various remediation and revegetation techniques for uranium-polluted soils.”

[Cathleen Genova @ Cell Press]

But it’s not just weight gain that poses a risk. People who are underweight also have an elevated risk of dementia, unlike people who are normal weight or overweight.

US researchers carried out a detailed review of 10 international studies published since 1995, covering just over 37,000 people, including 2,534 with various forms of dementia. Subjects were aged between 40 and 80 years when the studies started, with follow-up periods ranging from three to 36 years.

The review, which included studies from the USA, France, Finland, Sweden and Japan, also included a sophisticated meta-analysis of seven of the studies, published between 2003 and 2007 with a follow-up period of at least five years.

All kinds of dementia were included, with specific reference to Alzheimer’s Disease and to vascular dementia — where areas of the brain stop functioning because the blood vessels that supply them are damaged by conditions such as high blood pressure or heart disease.

“Our meta-analysis showed that obesity increased the relative risk of dementia, for both sexes, by an average of 42 percent when compared with normal weight” says Dr Youfa Wang, Associate Professor of International Health and Epidemiology at Johns Hopkins Bloomberg School of Public Health, Baltimore.

“And being underweight increased the risk by 36 percent.

“But when we looked specifically at Alzheimer’s Disease, the increased risk posed by obesity was 80 percent. The increased risk for people with vascular dementia was 73 percent.

“The risks were greater in studies where sufferers developed Alzheimer’s Disease or vascular dementia before the age of 60 or in studies with follow-up periods of more than 10 years.

“We also found that obesity was more likely to be a risk factor for women when it came to developing Alzheimer’s Disease and for men when it came to vascular dementia.”

The authors estimate that 12 percent of the dementia risk in the study population could be attributed to obesity, with this rising to just over 21 percent in patients with Alzheimer’s Disease.

It’s estimated that up to 10 percent of people aged 65 or more suffer from some form of dementia and two-thirds of those have Alzheimer’s Disease.

“There has been controversy about the links between obesity and dementia for a number of years, but previous findings have been mixed and inconclusive” says Dr Wang.

“The advantage of carrying out a meta-analysis is that it provides researchers with access to a large number of study subjects and it is possible to iron out the inconsistencies and come to overarching conclusions.

“Our detailed analysis clearly shows a U-shaped relationship between weight and dementia, with people who are obese or underweight facing a greater risk.

“We believe that our results show that reducing the prevalence of obesity is a promising strategy for preventing the progression of normal ageing into Alzheimer’s Disease.”

[Annette Whibley @ Wiley-Blackwell]