Diet sodas and increased stroke risk: Industry questions validity of large scale observational study

18 Feb 2019 --- Opting for artificially sweetened diet drinks two or more times per day could increase the risk of stroke by 23 percent, as well as raise the risk for other CVD outcomes in postmenopausal women. This is according to an observational study published in an American Heart Association (AHA) journal. The findings come at a time where the sugar substitute market has been boosted by rising concern about obesity and diabetes as well as government-imposed pressure that has thrown the spotlight on sugar consumption. However, industry experts have refuted the study, citing a lack of evidence and generalizability.

According to the findings, compared with women who consumed diet drinks less than once a week or not at all, women who consumed two or more ASB’s per day were:

• 23 percent more likely to have a stroke;
• 31 percent more likely to have a clot-caused (ischemic) stroke;
• 29 percent more likely to develop heart disease (fatal or non-fatal heart attack); and
• 16 percent more likely to die from any cause.

The impact of a heavy diet drink intake – defined as two or more times daily – more than doubled the stroke risk in women who had previously had heart disease or diabetes, obese women with a history of heart disease or diabetes and African-American women without previous heart disease or diabetes.

Researchers analyzed data on 81,714 postmenopausal women (age 50-79 years at the start) participating in the Women's Health Initiative study that tracked health outcomes for an average of 11.9 years after they enrolled between 1993 and 1998. At their three-year evaluation, the women reported how often in the previous three months they had consumed diet drinks such as low calorie, artificially sweetened colas, sodas and fruit drinks. The data collected did not include information about the specific artificial sweetener the drinks contained.

The results were obtained after adjusting for various stroke risk factors such as age, high blood pressure and smoking. These results in postmenopausal women may not be generalizable to men or younger women and the study is also limited by having only the women's self-report of diet drink intake.The impact of a heavy diet drink intake – defined as two or more times daily – more than doubled the stroke risk in women who had previously had heart disease or diabetes.

The study, published in Stroke, is one of the first to look at the association between drinking artificially sweetened beverages (ASB) and the risk of specific types of stroke in a large, racially diverse group of post-menopausal women. While this study identifies an association between diet drinks and stroke, it does not prove cause and effect because it was an observational study based on self-reported information about diet drink consumption. The study also did not distinguish between types of drinks and therefore cannot determine which artificial sweeteners may be more or less harmful than others. It also remains unclear as to how generalizable these findings are to other parts of the population.

Should we stop drinking diet sodas?
The AHA recently published a science advisory that found there was inadequate scientific research to conclude whether low-calorie sweetened beverages alter risk factors for heart disease and stroke in young children, teens or adults. The Association recognizes diet drinks may help replace high calorie, sugary beverages, but recommends water (plain, carbonated and unsweetened flavored) as the best choice for a no calorie drink.

“Unfortunately, current research simply does not provide enough evidence to distinguish between the effects of different low-calorie sweeteners on heart and brain health. This study adds to the evidence that limiting use of diet beverages is the most prudent thing to do for your health,” says Rachel K. Johnson, Ph.D., R.D., Professor of Nutrition Emeritus, University of Vermont and the Chair of the writing group for the AHA’s science advisory, Low-Calorie Sweetened Beverages and Cardiometabolic Health.

Responding to the study, the British Soft Drinks Association’s (BSA) Director General, Gavin Partington, said in a statement: “This study claims association between diet drinks and increased risk of stroke, but does not provide evidence of cause. According to all leading health authorities in the world, including the European Food Safety Authority (EFSA), low- and no-calorie sweeteners are safe. In March 2017, the UK Government and Public Health England (PHE) publicly endorsed the use of low-calorie sweeteners as a safe alternative to reduce sugar in food and drink and help people manage their weight.”

At the same time, the International Sweeteners Association (ISA) enforced that recent reviews commissioned by the World Health Organisation (WHO), indicate that there is no evidence that low-calorie sweeteners could cause or increase the risk of cardiovascular disease.

The ISA also note that the study in question is only observational and therefore has certain limitations, including the possibility of reverse causality and of residual confounding factors that might affect the reported associations as well as self-misreporting of intake data. 

Additionally, women who reported higher consumption of low-calorie beverages were more likely to be obese, past smokers, hypertensive, with poorer diet quality and higher overall energy intake, and thus more likely to have (undetected) diabetes, showing that there could be other unmeasured factors to confound the relationship between low-calorie beverages and heart disease. 

“Indeed, there is a drastic fall in the hazard ratios (HRs) after allowance for covariates. This indicates that more precise and valid adjustment for confounding items would likely imply a further decrease in the association. In addition, there was no trend in risk with dose,” says Dr. Carlo La Vecchia, Professor of Epidemiology at the University of Milan, in the ISA statement.

While PHE shares: “Findings from this study should be interpreted with caution since it is an observational study and suffers from inherent limitations of observational research. In observational studies, it is difficult to establish causality. Such studies can also be subject to confounding and it is possible that an observed effect is caused by another unidentified factor.”

Research in the area of sweeteners and human health is somewhat murky. These findings follow that of the British Medical Journal (BMJ) from earlier this year that highlighted that there was no compelling evidence that non-sugar sweeteners (NSSs) improve health or help people to lose weight. The review, which was prepared to inform the upcoming World Health Organization (WHO) guideline on NSSs usage, analyzed 56 studies comparing no intake or lower intake of NSSs with higher intake in healthy adults and children. Most health outcomes did not display differences between the NSS exposed and unexposed groups in adults or children. This was true for body weight, diabetes or glycemic control, appetite, blood pressure and bladder or lower urinary tract cancer risk, according to the review.

The BMJ published study further noted that there is a lack of quality research in the area of health and artificial sweeteners. 

By Laxmi Haigh