Cells may age faster in obese teenagers who have a very salty diet, according to new research presented at the American Heart Association's Epidemiology & Prevention/Nutrition, Physical Activity and Metabolism Scientific Sessions 2014.
Experts already know that the protective ends on chromosomes - called telomeres - shorten as we age, and that some physical and lifestyle factors can cause this shortening to become advanced. These factors include smoking, a lack of physical activity and having high body fat.
The new research, though, is the first study to find that sodium intake also has an impact on telomere length.
To examine the extent to which telomere length is influenced by an interaction of sodium intake and body fat, the researchers divided 766 teenagers between 14 and 18 years old into two groups based on their diet.
The teenagers who were in the lowest half of reported sodium intake consumed an average of 2,388 mg of sodium per day, whereas the teens in the highest half of reported sodium intake consumed an average of 4,142 mg per day.
Even the teens in the lower sodium group were consuming much more salt than the American Heart Association's recommended 1,500 mg per day, however.
To what extent did weight influence telomere length in teens with high sodium intake?
The researchers used a type of ratio called "T/S ratios" to describe the relationship between the length of a telomere compared with the length of a single gene.
They found that the T/S ratio in obese teens with a high sodium intake was 1.24 versus 1.32, while the T/S ratio of normal-weight teenagers with a high sodium intake was 1.29 versus 1.30.
This shows that the telomeres were significantly shorter in obese teens who had a high sodium intake. But in the teens of a normal weight who had a high sodium intake, there was no significant difference in telomere length.
- The average American consumes about 3,400 mg of sodium a day.
- More than 75% of our sodium consumption comes from processed and restaurant foods.
- The six most popular foods containing high levels of sodium are breads, cold cuts and cured meats, pizza, poultry, soup and sandwiches.
"Even in these relatively healthy young people, we can already see the effect of high sodium intake, suggesting that high sodium intake and obesity may act synergistically to accelerate cellular aging," says Dr. Haidong Zhu, lead author of the study and assistant professor of pediatrics at Medical College of Georgia, Georgia Regents University in Augusta.
Obesity increases sensitivity to salt and also causes inflammation. This might explain why having a high sodium intake had such a pronounced difference in the overweight teens.
"Lowering sodium intake may be an easier first step than losing weight for overweight young people who want to lower their risk of heart disease," Zhu says.
"The majority of sodium in the diet comes from processed foods, so parents can help by cooking fresh meals more often and by offering fresh fruit rather than potato chips for a snack."
Other findings presented at the American Heart Association meeting included research on how a behavioral intervention can encourage adults to reduce the amount of sodium in their diet. The intervention involves using more herbs and spices in food as an alternative to salt.