Claims blood test predicts lifespan are exaggerated
The Mail Online promises us a “revolutionary blood test that could predict how long you'll live, what ailments you'll get – and how fast you'll age”.
The Mail is not the only news organisation to make such elaborate claims. However, they are all based on a misunderstanding of some complex science looking at whether chemicals found in our blood are associated with our age.
In the study, researchers analysed the blood samples from twins on the Twins UK registry, to identify which of a large range of ‘metabolites’ were associated with the twins’ ages. The researchers found that 22 of these metabolic chemicals were associated with age (older people tended to have higher levels of these metabolites).
One metabolite in particular, C-glyTrp, was particularly strongly associated with age-related factors such as bone density and lung function.
However, as the researchers say, their study does not prove that C-glyTrp or any of the other metabolites are directly responsible for the differences in ageing.
While it makes for great headlines, there is currently no blood test that could predict your lifespan or what illnesses you will suffer; nor did this research attempt to discover one.
Where did the story come from?
The study was carried out by researchers from the Department of Twin Research and Genetic Epidemiology, King’s College London, and other researchers in Germany, Australia and Qatar, and received support from Roche Diagnostics Australia Pty Ltd. Some of the researchers involved in the study are employed by the pharmaceutical industry.
The study was published in the peer-reviewed medical journal, International Journal of Epidemiology.
Most of the UK media have exaggerated the findings of this research, which do not suggest that a ‘revolutionary blood test’ could be on the way. It is worth pointing out that the well-written press release issued about this research makes no such claims, and that journalists have made a leap of the imagination to create a scoop from this study.
What kind of research was this?
This was a cohort study that set out to examine whether certain metabolites in the blood are associated with ageing. Human ageing is a complex process believed to be influenced by genetic, lifestyle and environmental factors.
The researchers say that past research suggests genetics only explains around a quarter of variation in human survival up to the eighth decade (age 70-80). This implies that molecular changes related to environment and lifestyle could be involved.
The researchers aimed to explore the biochemistry of ageing and identify molecular changes associated with ageing and age related traits.
What did the research involve?
The research first used a national register of twins (the Twins UK registry) which had blood chemical profiles available for 6,055 sets of twins.
Twin studies can be particularly useful, as identical twins are genetically identical, so the effects of environmental factors are easier to spot.
The researchers collected information about the physical and biochemical characteristics of the twins, including:
- Body mass index (BMI)
- two measures of lung function: the amount of air they could forcefully exhale in one second (FEV1), and total volume of air they could breathe out (FVC)
- bone mineral density at the hip
- blood pressure
- cholesterol
- telomere length (a marker of biological ageing)
- blood levels of dehydroepiandrosterone sulphate (DHEAS, a marker of biological ageing)
They measured the levels of 280 known metabolites in the blood samples from the twins and used statistical models to identify which metabolites could be associated with chronological age.
They then looked at whether the group of metabolites found to be associated with age were also associated with mortality, and with each of the different physical and biochemical characteristics measured.
To confirm this finding, the researchers looked at whether the same metabolites were found to be associated with age and FEV1 in a separate cohort. This separate cohort involved 887 people drawn from the Augsburg region of Germany, who had their blood samples taken and FEV1 measured.
They also carried out further analyses in the identical twin samples. This was to see whether levels of the metabolite most strongly associated with age differed among identical twins who had been born of different birthweight.
What were the basic results?
In their initial tests on the large UK cohort, the researchers identified 22 metabolites associated with chronological age, and with the other physical and biochemical markers of ageing that had been examined. One metabolite in particular, C-glycosyl tryptophan (C-glyTrp), was found to be strongly associated with age and also to FEV1 and bone mineral density. Examination of the separate German cohort replicated these findings. C-glyTrp was also strongly associated with lower weight at birth which has previously been shown to be a determinant of poorer health status in mid life and old age.
Further analysis of identical twins from the Twins UK registry who were of different birthweight suggested that the difference in C-glyTrp levels could be due to a non-genetic explanation. The difference appeared to be influenced by early development.
How did the researchers interpret the results?
The researchers say that their data demonstrates that profiling metabolic chemicals in blood samples can suggest key molecular mechanisms that may produce physiological changes and influence long-term health and ageing. But this study did not demonstrate causality (a cause and effect relationship).
Conclusion
This is an interesting study which identifies a profile of 22 metabolic chemicals associated with chronological age in humans. These 22 chemicals are also associated with several other age related traits, such as lung function and bone mineral density. One metabolite in particular, C-glyTrp, was found to have particularly strong association. The researchers also observed that differences in the blood levels of this metabolite may account for a small portion of the difference in birthweight between identical twins.
However, as the researchers say, their study does not prove that C-glyTrp or any of the other metabolites are directly responsible for the differences in these markers of ageing. Other factors could be involved.
Despite the media’s elaborate claims that measuring these metabolites could ‘predict how long you'll live and what ailments you'll get’ this study has not measured associations with health, disease or life expectancy. As the researchers themselves acknowledge, birthweight was the only ‘life measure’ they had information available on.
The researchers also note that the majority of their twin study (93%) were women, meaning the results may not apply to men in the same way. Their results have been verified in only one other small cohort, in which information on other health data was unavailable.
Overall, this is interesting early research examining the biology of ageing. However, the study makes no claims that a blood test could be on the way to predict your future health and your rate of physical ageing.
