Fizzy drinks age you faster? Load of gas

Fizzy drinks age you faster? Load of gas

Soft drinks might age you as much as smoking does. This was how the media reported a study published recently in the prestigious American Journal of Public Health. And the media did get it right: The paper did come up with that finding.

It was published in a top journal, with molecular biologist Elizabeth Blackburn of the University of California at San Francisco as one of its authors. She shared the Nobel prize in medicine with two others in 2009 for pioneering work on telomeres.

A telomere is a loop found at the tip of each chromosome, and it prevents genes from being lost during cell division. It is like the plastic tip at the end of a shoelace - it protects the chromosome tip from fraying, which is important because broken DNA tips left unrepaired lead to cell death.

Because cells must be replaced over time, they divide. But because telomeres get shorter with each cell division, they eventually become too short. When that happens after repeated divisions, the cell cannot divide any more, so it dies off.

Some scientists, notably those linked to the Blackburn lab, argue that this causes ageing. But there is no evidence to show that this is a cause rather than an effect of ageing. In fact, telomere shortening might have no link to ageing itself.

Such scientists are using telomere length as a biomarker for ageing. In their small studies, they have even managed to link telomere length to blood pressure, lung function, cognitive function, hand grip strength (as a measure of general health) and various other clinical outcomes.

But before something can be used as a biomarker for a certain condition, different labs must be able to show that it works in multiple studies and different populations. However, telomere length has been shown to be reliably associated with age, sex and race only, but not any clinical outcomes.

It is well established that telomeres are shorter in males and older people. Of course, older males do tend to have shorter life expectancies. However, telomeres are also shorter in white people than in non-whites, but whites do not have shorter life expectancies than non-whites.

So there is no consistent relationship between telomere length and longevity. In fact, the telomeres in seabirds called storm petrels, which can live up to 40 years, even lengthen with age.

Nevertheless, some scientists, like those who published the recent study, continue to push the telomere shortening model of ageing and health outcomes. However, other scientists have not been able to replicate their results in large studies and good meta-analyses that have been published.

In the recent study, the raw data actually showed a correlation between people who drank more soda and longer - not shorter - telomeres. But when age, sex and race were factored in, that correlation quickly disappeared. This means that the study showed no association between soda consumption and telomere length. Yet, the scientists managed to make the study say the exact opposite.

They reclassified the beverages into two types: fizzy and non-fizzy - whereupon a correlation was found between the consumption of fizzy soda and telomere shortening.

They concluded that "a daily 20-ounce (0.57 litre) serving, the current standard serving size (of a fizzy soda drink, leads to) 4.6 additional years of ageing" - which they said was what smoking 20 cigarettes a day did to people as well.

So fizzy soda apparently shortens life as much as cigarettes do. But it is biologically implausible that adding carbon dioxide to sugary soft drinks to make them fizzy will age us faster, whereas non-fizzy sugary soft drinks on their own will not.

As any secondary school chemistry textbook will tell you, carbon dioxide, sugar and water are inert. In other words, there is virtually no chemical reaction when they are mixed together. No new compounds are produced, so if you drink such a mixture, it has no new adverse effects compared with taking just sugar and water without the gas.

Thus, it is incumbent on the researchers to offer a reasonable hypothesis as to why adding fizz changes a sugar solution so very drastically.

Smoking kills four times as many people as obesity does every year, even if all cases of obesity were caused solely by drinking fizzy soft drinks.

Dr Blackburn co-founded a diagnostic firm with Dr Elissa Epel, a psychologist and one of the co-authors of the recent paper. The firm, called Telomere Health, offered to measure the length of your telomeres so you might acquire "unique knowledge about disease risk and your rate of biological ageing". But the two have sold their shares in the firm, which has been renamed Telomere Diagnostics. Another co-author of the study, Dr Jue Lin, continues to have a financial stake in the lab.

In March last year, Dr Blackburn and Dr Epel snagged a million-dollar deal at the London Book Fair to write a book titled The Telomere Solution: How The Nobel-Prize-Winning Discovery Can Help You Fight Cellular Ageing And Improve Lifelong Health.

However, the telomere model of ageing is not one that is supported by enough research just yet. And it does seem highly unlikely that fizzy drinks cause people to age faster, or that they kill as many people, or as certainly, as smoking does.

andyho@sph.com.sg


This article was first published on Feb 5, 2015.
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