: and why fly research does not always translate to humans.
We all have heard, or read, that the lifespan of humans has steadily climbed over the centuries and the recent decades. This trend is generally true, but not absolute.
The latest research published in the May 14, 2008 issue of PLoS ONE (complete text freely available) indicates that the death rate of Americans with 16 or more years of education has decreased (age standardized) from 1993 to 2001 – meaning an increase in lifespan. However, the death rate for those with less than high school education has DECREASED over this same time period.
For example white women with the least education had an 3.2% per year INCREASE in all cause death rate, while high school educated white women still had a 0.7% per year INCREASE in death rate.
How can this happen with the continued advancement of the medical profession and technology, along with an increase in the nation’s prosperity? Sure, we might agree that the difference in economic conditions between the relatively highly educated group and the lower educated group would bring about a difference in access to health care. But then you would just think that the highly educated population would have relative greater longevity gains, as compared to the less educated. However, it does not make sense that the death rate is increasing – hence shorter lifespan – for the less educated in the time period between 1993 and 2001.
Is there any logic beyond the greater and better access to health care that the wealthy well educated have at their disposal to account for their greater increase in lifespan (decreased death rate)?
What if we tired to account for the general economic conditions and instead of looking at educational level achieved we examined straight intelligence (as measured by IQ tests – not perfect, but a standardized measurement). A review paper (full paper available here) follows a study based in Scotland, which examined childhood IQ scores and death rates and found that IQ scores predict differences in adult death. The relationships between higher IQ scores and lower death rate held up when taking into account socioeconomic variables. Here is a link to another paper by one of the same authors (Linda Gottfredson) as the previous paper with further insight into this subject matter.
Still these set of data leaves some doubt about the separation of nature and nurture (and it does not speak to the alarming trend of decreased lifespan in lower educated individuals). Is there any molecular evidence for intelligence making a difference in lifespan?
Researchers in Italy in a 2008 paper found that a gene called SSADH (Succinic Semialdehyde Dehydrogenase) might play a role both in intelligence and lifespan (pubmed link). Those people with the ‘less intelligent’ version of the gene were unlikely to live to 85 years old, while those with the ‘smart’ version had a greater probability of living to 100 as reported here. How might SSADH help both intelligence and lifespan? SSADH is known to ‘detoxify’ the brain by reducing excess acid, which is argued could protect brain cells thereby resulting in protecting the ‘body’. The researchers also tested the intelligence of 65 to 85 year olds and found that those with at least one version of the less intelligent version performed worse than the other groups.
This work confirmed previous work by professor Robert Plomin, who originally found the link between intelligence scores and variations of the SSADH genes in younger age groups (but the effect was small).
Dr Plomin also pointed out:
“There’s no doubt that lifestyle, such as reading, having challenging work and enriching your cultural life, is far more important than having the bad variant,”
These comments I would highly agree with and have pointed out several times in previous posts (here, here). Additionally, you can’t do much about the shuffle of genes you were dealt, but you do have control over the lifestyle choices you make – so make good ones.
What happens when we look at recent research on intelligence and lifespan in lower organisms?
Using flies, two scientists at the University of Lausanne (Tadeusz Kawecki and Joep Burger) in 2008 discovered a negative correlation between improvement in mental capacity and the flies’ lifespan – as in the smart flies died younger (pubmed link).
They used two groups; one group were left in a ‘natural state’, while in the other they boosted intelligence by Pavlovian methods – associating smell and taste with particular food or experiences (thanks JB for pointing out this paper). They used these ‘teaching’ methods over numerous generations (30-40) which led by artificial selection to flies that learned at a quicker rate and remembered longer than those left in the ‘natural’ state. What they found was the natural flies lived 80-85 days, but the selected and trained smart ones only live 50-60 days.
These results would be exactly opposite of the research pointed out above in humans. But I think the researchers left out a vital control, or where unaware of a series of research articles. Previous work found that the simple exposure of flies to food odorants can reduce lifespan (Libert et al., 2007), and taking out specific gustatory or olfactory neurons can extend lifespan (Alcedo and Kenyon, 2004). So is it possible that all the exposure to smell and taste as part of their teaching method could have played a role in the reduced lifespan? But then it could be argued this should have also happened in the first generation of animals they tested with method – but I do not have access to this data set.
Either way, what we learned in the fly in this case does not appear to translate to the human situation.
Is there any other global human data out there that might offer an argument one way or the other regarding intelligence and lifespan – and what does this mean for America?
While America is obviously is the most powerful nation in the world, with the largest economy, along with the most advanced medical technology is would seem obvious that they should have the longest lifespan – no?
The reality of the situation is that America is not even in the top ten nations (nor top 20 or even 30) for lifespan.
According to the 2008 World Health Organization (WHO) data, the citizens of America expected lifespan, for both sexes, is 78 years.
There were 31 countries that have higher lifespans than USA, which included: Andorra, Australia, Austria, Belgium, Canada, Cyprus, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Israel, Italy, Japan, Luxembourg, Malta, Monaco, Netherlands, New Zealand, Norway, Portugal, Republic of Korea, United Kingdom, United Arab Emirates, Sweden, Switzerland, Spain, Singapore, and San Marino.
Now some on this list you might have expected (Northern European countries), but not all of them. Does this somewhat shock you? How can America the most advanced, richest nation in the world be only rank 31st on lifespan? Now look at the five countries that equaled America’s lifespan of 78 years: Chile, Slovenia, Costa Rica, Cuba, and Kuwait. Does this make you even wonder more?
Now does the longevity data correlate with the ‘intelligence’ scores? Well at least for USA it appears to, as rankings in a number of ‘intelligence’ scores look like they correlate with similar ranking in the lifespan list.
The Organization for Economic Cooperation and Development does standardized testing of developed countries to be able to compare across these nations. The Program for International Student Assessment (PISA) test 15 year olds every 3 years in science, reading, and math. The results indiciate consistent mediocre scores for Americans (This is only one example of these types of tests – but I am sure you have come across similar reports in the press with America further down the ranking than you would expect for all its economic strength).
Look here for the PISA rankings in 2003
And here are the 2006 science results in pdf format.
58 developed countries were included in the linked 2006 science scores and USA placed 29th out of the 58. And if you glance at the link the majority of the countries that performed better than USA were also on the list of the countries that lived longer (Finland, Canada, Japan, New Zealand, Australia, Netherlands, Korea, Germany, United Kingdom, Switzerland, Austria, Belgium, Ireland, Sweden, Denmark, France,and Iceland). Additionally, not all the countries that had a longer lifespan than USA were involved in the above study.
While it is far from a perfect correlation and this is only one measure of education/intelligence it is enough food for thought. I wonder if somebody formally tested various intelligence scores and lifespan would they find a statistical correlation? Guess we will just have to wait until someone examines this.
What is my conclusion of all this rambling? It appears educated and intelligent people may live longer than less intelligent or less educated people (and that research with lower organism do not always translate to humans for various reasons). While socioeconomic conditions may play a large role in lifespan differences there may be a more general molecular mechanism playing a part. Currently we may only have a few candidate molecules (I only report one here as an example, but there are others) future research will further tease out potential molecules.
As for America maybe it is time for a little re-thinking on the education and health of this nation. The mediocre rankings in both lifespan and standardized ‘intelligence’ tests is not encouraging (possibly even embarrassing) for the most powerful country in the world.
What does this mean to you as an individual ? You must remember that intelligence is only partially inherited, and at least equally influenced by the environment (education, etc). While we currently can not readily change our genetic makeup we can have an influence on how we live our lives – keep on learning – get an education. Live an enriched life, never stop learning, keep the brain active. Pretty simple advice. What is good for your brain is good for your health (lifespan) – and vice versa.
What did you learn today?
(There is reasonable evidence regarding how an ‘active’ brain can buffer against many brain diseases and I will do my best to cover this at another time).