Can soft drinks speed aging?

Soft drinks may quench your thirst and provide an energy boost. They also can do a lot of damage — beyond expanding your waistline. Drinking sweetened sodas daily can speed how fast the body’s cells age, a new study indicates.

Regularly downing sugary soft drinks can boost the risk of chronic diseases, including type 2 diabetes, heart disease and liver disease. These long-lasting conditions have no cure. Today, three-fourths of all American healthcare dollars go to manage such ailments. What researchers hadn’t worked out was why overindulging in sugary drinks leads to such diseases. 

Researchers at the University of California, San Francisco, or UCSF, wondered if the link might lie with a marker of cellular aging. It’s called the telomere. Telomeres are the repeated sequences of DNA that cap the ends of our chromosomes. Like the plastic tips that keep shoelaces from fraying, telomeres protect our DNA from damage, explains UCSF’s Cindy Leung. As an epidemiologist, she probes the links between diet and health.

Telomeres shorten each time a cell divides. But “if the telomere gets too short,” she notes, “the cell can stop dividing and die.” As such, telomere shrinkage is said to reflect — and possibly even determine — a cell’s biological age. Studies show that shorter telomeres also raise a person’s risk for diabetes, heart disease and some cancers.

To scout for a link between sugary beverages and telomere length, her team combed through a lot of health data. These came from a nationwide survey of 5,309 U.S. adults between 1999 and 2002. (This survey has been ongoing since the early 1960s. Over its history, it has collected health data on more than 140,000 people.) At mobile exam centers, survey participants get their height and weight measured, give blood samples and answer questions about their lifestyle and other behaviors. During those interviews, each volunteer also reports everything he or she had eaten or drunk in the past day.

From this information, Leung’s team calculated how much sugar from beverages each volunteer had consumed. But since a one-day report doesn’t always reflect general habits for all other days, the scientists also asked about factors that can vary among participants. Such variables included their age, gender, what ethnic group they belonged to, whether they were married, where they live, whether they smoke and if they had been surveyed on a weekday or weekend. Many of these factors can affect how well the single-day report reflects a person’s usual habits.

The other piece of information that Leung’s team needed was telomere lengths. To measure them, they extracted DNA from each participant’s blood. Then they ran those samples through a test, or assay. It looked for a special, repeated stretch of six DNA building blocks, called nucleotides. This particular combo of six nucleotides is found only in human telomeres, not in the rest of our chromosomes’ DNA.

Leung’s UCSF coworker, Elizabeth Blackburn, shared the 2009 Nobel Prize in Medicine for discovering how chromosomes are protected by telomeres. Members of Blackburn’s lab assayed the telomeres for the new study.

Then the researchers determined how average telomere length varied depending on traits and behaviors such as age, race, how much someone exercised and how much schooling they’d had. Then, taking this information into account, the scientists homed in on the variable they wanted to study — daily intake of sweet drinks. They looked at soft drinks sweetened with sugar, sweet non-carbonated beverages (such as sports drinks), diet soft drinks and fruit juices.

After crunching the numbers, “drinking an 8-ounce serving of soda was associated with 1.9 additional years of cellular aging,” Leung told Science News for Students. That means people who guzzle a 20-ounce bottle of some sugary soft drink daily are inflicting roughly 4.6 additional years of biological wear and tear on their cells. About one-fifth of study participants reported drinking at least 20 ounces of sweetened soft drinks each day. Leung’s team reported its findings October 16 in the American Journal of Public Health.

Complicating the picture

Tim Spector expressed caution about interpreting the findings. He’s an epidemiologist at King’s College London, in England. His team found shorter telomeres in women who were obese or who smoked cigarettes. “Telomeres are affected by so many things — social class, smoking, diet, race, gender, the speed at which your blood cells divide. Nearly everything has a small effect,” he says. That’s what makes these studies “very tough.”

In a 2008 study, for instance, Blackburn and her coworkers reported that good habits can lengthen telomeres. They studied a three-month regimen in people. It consisted of eating healthy, getting regular exercise, not smoking, getting social support and managing stress.

Looking at the UCSF study, Spector wondered why drinking fruit juice showed no link to shorter telomeres. Drinking sugary soft drinks did. “Fruit juice is high in fructose, as are sugar-sweetened beverages. Both are chemically similar,” he notes.

One possible explanation: Maybe people who drink fruit juice differ in other ways from those who prefer sugary soft drinks. These differences could include cultural habits, education, income or overall diet choices. Those factors might explain the groups’ telomere differences, he says. Another possibility: “Maybe you can rescue drinking lots of Coke with the fiber in fruit juice,” Spector speculates.

Or perhaps the study didn’t detect a telomere effect with fruit juice because participants simply didn’t drink enough of it, compared with sugary soft drinks. Participants downed, on average, about 12 ounces of sugary sodas per day, but only 4 ounces of juice and other non-carbonated sugary drinks. Even though all these drinks are similarly sugary, Leung explains, “we think maybe there was a threshold effect.” What she means: No effect may appear until someone has drunk a certain amount.

Right now, sports drinks and energy drinks are on the rise, particularly among teens and young adults. That is why Leung suspects that “if we were to repeat the study today, we would expect to see the same association (with shorter telomeres) that we found with sugary sodas, in all these other sugary drinks.”

Not-so-sweet science

On November 10, other UCSF health scientists — along with researchers at the University of California, Davis, and Emory University School of Medicine in Atlanta, Ga. — launched a new website called SugarScience. A 12-member team of researchers reviewed some 8,000 scientific papers on the health effects of added sugar. The new website summarizes what the team learned.

Among its key findings: The average American consumes 82 grams (19.5 teaspoons) of sugar each day. The American Heart Association recommends no more than 9 teaspoons a day for men and no more than 6 teaspoons a day for women and children. A typical 12-ounce sugary soft drink contains 46.2 grams (11 teaspoons) of sugar.

What’s more, manufacturers add sugar to 74 percent of the packaged foods sold in grocery stores, the studies showed. “So, even if you skip dessert, you may still be consuming more added sugar than is recommended,” the researchers conclude. These and other “added” sugars — those not present naturally in the fruits, grains or other constituents of foods — really add up. On average, the website notes, today’s “Americans consume 66 pounds [30 kilograms] of added sugar each year.”

Readers can submit questions to the website’s team of experts. Some visitors already have asked how to cut back on sugar and how quickly they might see health benefits if they do.

Power Words

behavior  The way a person or other organism acts toward others, or conducts itself.

cancer  Any of more than 100 different diseases, each characterized by the rapid, uncontrolled growth of abnormal cells. The development and growth of cancers, also known as malignancies, can lead to tumors, pain and death.

carbonation  The process of pumping carbon dioxide into a liquid, to imbue that liquid with bubbles. It gives the now-carbonated liquid a fizzy taste.

cell  The smallest structural and functional unit of an organism. Typically too small to see with the naked eye, it consists of watery fluid surrounded by a membrane or wall. Animals are made of anywhere from thousands to trillions of cells, depending on their size.

chromosome  A single threadlike piece of coiled DNA found in a cell’s nucleus. A chromosome is generally X-shaped in animals and plants. Some segments of DNA in a chromosome are genes. Other segments of DNA in a chromosome are landing pads for proteins. The function of other segments of DNA in chromosomes is still not fully understood by scientists.

constituent  An ingredient or building block of some material.

diabetes  A disease where the body either makes too little of the hormone insulin (known as type 1 disease) or ignores the presence of too much insulin when it is present (known as type 2 diabetes).

DNA  (short for deoxyribonucleic acid) A long, double-stranded and spiral-shaped molecule inside most living cells that carries genetic instructions. In all living things, from plants and animals to microbes, these instructions tell cells which molecules to make.

epidemiologist  Like health detectives, these researchers figure out what causes a particular illness and how to limit its spread.

fructose  A simple sugar that (along with glucose) makes up half of each molecule of sucrose, also known as table sugar.

liver  An organ of the body of animals with backbones that performs a number of important functions. It can store fat and sugar as energy, breakdown harmful substances for excretion by the body, and secrete bile, a greenish fluid released into the gut, where it helps digest fats and neutralize acids.

nucleotides  The four chemicals that link up the two strands that make up DNA. They are: A (adenine), T (thymine), C (cytosine) and G (guanine). A links with T, and C links with G, to form DNA.

telomere   A natural protective “cap” on the ends of chromosomes, made by successions of a six-nucleotide sequence of chemicals. This chemical sequence is found only on the ends of chromosomes. It’s known as TTAGGG, where each T corresponds to a molecule of thymine, each A is a molecule of adenine and each G is a molecule of guanine. Over time, telomeres shorten as the cell they’re in copies itself. If the telomere length gets too short, the cell stops dividing and dies.

variable (in experiments) A factor that can be changed, especially one allowed to change in a scientific experiment. For instance, when measuring how much insecticide it might take to kill a fly, researchers might change the dose or the age at which the insect is exposed. Both the dose and age would be variables in this experiment.