Monday, September 09, 2013

Could GOOD hygiene cause Alzheimer's? People in wealthy countries are at 'greater risk' as they have less contact with bacteria

That hygeine hypothesis won't die, regardless of the evidence against it.  Tribal Aborigines in Australia, for instance, live in very dirty conditions  -- yet have high rates of autoimmune disease such as asthma and diabetes

The article is nonetheless a brave attempt to use official data to examine an hypothesis.  I think that the difficulties of doing that do defeat then in the end, however. They had three indices related to Alzheimer's.  I quote:  "The WHO report presents three variables related to AD: age-standardized DALY, age-standardized deaths, and DALY for age 60+. There is low correlation between these three measures (linear regressions after necessary data transformations had R-squared values 0.040; 0.089; 0.041)." 

Those correlations are effectively zero.  So measures that should have at least been highly correlated were not.  Choosing just one and running with it is therefore suspiciously like data dredging and fails to address the question of its validity.  I would conclude nothing from this research.

The journal article is Hygiene and the world distribution of Alzheimer's Disease

An obsession with being too clean and hygienic could lead to a higher risk of dementia, researchers have warned.

Their study pinpointed a significant relationship between a nation’s cleanliness and the number of Alzheimer’s patients.   Countries which can afford better sanitation have higher rates of the disease.

The study found a 'very significant' relationship between a nation's wealth and hygiene and number of Alzheimer's patients within a country's population

So Britons and inhabitants of other developed nations were around ten per cent more likely to suffer dementia than those in countries like Kenya and Cambodia.

The researchers suggested the ‘hygiene hypothesis’ was behind the difference. This is the theory that an excessively clean lifestyle leaves our immune systems out of balance and unable to combat many germs.  It has already been linked to the rise in the number of allergies, such as asthma and eczema.

One in three Britons over 65 will develop dementia. Alzheimer’s and other forms of the condition blight the lives of more than 800,000, with 500 new cases each day.

Lead researcher Dr Molly Fox, from Cambridge University, said: ‘The hygiene hypothesis is well-established. We can now add Alzheimer’s to this list of diseases.

‘There are important implications, especially in developing countries as they increase in sanitation.’

The study of health data from 192 nations found those with a relatively low risk of infection had more patients with Alzheimer’s.

Likewise, better sanitation and urban living were linked with a higher incidence of the disease, irrespective of life expectancy. Taken together, these factors accounted for 42.5 per cent of the variation in rates of Alzheimer’s between countries.

Dr Fox said changes in diet, life expectancy and healthcare could not explain the differences.

The researchers found that exposure to germs throughout an individual’s lifetime, not just early on, may affect the risk of dementia.

A lack of contact upsets the development of white blood cells, particularly those called T-cells, which are a key part of the immune system.

This imbalance has been linked to the types of inflammation found in the brains of those with Alzheimer’s, said the report in the journal Evolution, Medicine and Public Health.

A spokesman for the Alzheimer’s Society said: ‘It is an interesting  theory. However, it is always difficult to pin causality to one factor.’

The best way to cut risk is to eat healthily, exercise, not smoke and keep blood pressure and cholesterol in check, he added.

Countries where more than three-quarters of the population are located in urban areas, such as the UK and Australia, had 10 per cent higher rates of Alzheimer’s compared to countries, such as Bangladesh and Nepal, where less than one-tenth of people inhabit urban areas.

Overall, differences in levels of sanitation, infectious disease and urbanisation accounted for 33 per cent, 36 per cent and 28 per cent of the variation in Alzheimer’s rate between countries.

Previous research has shown that Alzheimer’s affects fewer people in Latin America, China and India than it does in Europe.

Even within those regions, prevalence is lower in urban than in rural areas, according to the new findings.

The hygiene hypothesis is based on the assumption that lack of contact with 'dirt' in the form of bacteria and other infectious agents upsets the development of white blood cells, key elements of the immune system.

‘Exposure to microorganisms is critical for the regulation of the immune system,’ wrote the researchers.

They added that, since increasing global urbanisation beginning at the turn of the 19th century, the populations of many of the world’s wealthier nations have increasingly very little exposure to the so-called ‘friendly’ microbes due to ‘diminishing contact with animals, faeces and soil.’

‘The increase in adult life expectancy and Alzheimer’s prevalence in developing countries is perhaps one of the greatest challenges of our time,’ said Dr Fox.

The hygiene hypothesis is normally thought to be most relevant in childhood, when the immune system is still developing.

But in the case of Alzheimer’s, exposure to microbes across a person’s lifetime might be important, say the scientists.

This is because regulatory T-cell numbers peak at various points in life, for example at adolescence and middle age.

The results of the study are published by the journal Evolution, Medicine and Public Health.


A 'cure' for Down's syndrome? Scientists discover compound that reverses learning difficulties in mice

Only the beginning of a beginning

A compound that reverses Down’s syndrome-like learning disabilities has been identified.  Researchers used the compound to reverse learning disabilities in mice.  However, it only works when given to affected mice on the day of their birth.

The Down’s Syndrome Association has described the finding as of ‘great interest’ but recognises that it would not help people currently living with Down’s syndrome.

U.S. researchers, led by Professor Roger Reeves at the Johns Hopkins University School of Medicine, in Baltimore, identified the compound that dramatically boosts the learning ability and memory of mice with a Down’s syndrome-like condition.

They believe that a single dose encourages the cerebellum of the rodents’ brains to grow to a normal size - most people with Down's syndrome have a cerebellum that is only 60 per cent of the normal size.

After being injected with the compound, the rodents’ were able to function as well as mice without learning disabilities in behavioural tests.

The scientists have warned that use of the compound, a small molecule known as a sonic hedgehog pathway agonist, has not been proved safe for use in people with Down's syndrome, but say their experiments hold promise for developing drugs like it.

Carol Boys, chief executive of the Down's Syndrome Association, said: ‘Professor Reeves and his team are part of the respected worldwide Down's syndrome research community.  ‘This successful piece of clinical research will be of great interest to them all.

‘As Professor Reeves explains, this is not going to translate into clinical applications for people currently living with the condition but is another step along the path of understanding the complexity of an extra chromosome 21 in every single cell.’

Down's syndrome is a genetic condition that causes learning disabilities and a characteristic range of physical features.

Most children with the condition have reduced muscle tone, eyes that slant upwards and low birth weight.
The compound only works when administered on the day of birth. It works by enabling the cerebellum in the brain to grow to a normal size. Image shows the chromosomes of a person with Down's syndrome

The compound only works when administered on the day of birth. It works by enabling the cerebellum in the brain to grow to a normal size. Image shows the chromosomes of a person with Down's syndrome

They are also prone to a range of complications such as heart disorders, bowel and digestive problems, poor vision and hearing, thyroid dysfunctions and blood disorders.

The condition affects about 750 babies born in the UK every year.

It is caused by the presence of an extra copy of chromosome 21 in a baby's cells.


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