Higher consumption of artificially sweetened soft drinks was associated with an increased risk of both stroke and dementia in an analysis of more than 4,000 participants in the Framingham Heart Study Offspring cohort, researchers found.
In the observational study, those who drank at least one artificially-sweetened beverage a day were nearly three times more likely to develop ischemic stroke (HR 2.96, 95% CI 1.26–6.97) and 2.9 times more likely to develop Alzheimer's disease (95% CI 1.18–7.07) over 10 years than those who abstained, Matthew Pase, PhD, of Boston University School of Medicine, and colleagues reported in the American Heart Association's journal Stroke.
However, sugary beverages weren't tied to an increased risk of stroke or dementia -- a finding the authors called "intriguing," and one that could have been due to survival bias.
"It is possible that individuals with high intakes of sugary beverages may have died earlier from other illnesses such as heart disease," Pase told MedPage Today. "It is also worth noting that our sample consumed diet soda more frequently than sugar-sweetened soda and this may contribute to differences in findings between regular and diet soda."
He cautioned that the association between artificially sweetened drinks and stroke and dementia seen in their study does not imply causation -- a point emphasized by Marion Nestle, PhD, professor of nutrition, food studies, and public health at New York University, who wasn't involved in the study.
"Association is not the same as causation, although the survival curves are impressive," Nestle said. "I wish the authors had offered a plausible hypothesis for how artificial sweeteners could be causally related to stroke and dementia."
Several other experts commented on the "controversial but inconclusive" nature of the association.
"The relationship with artificially sweetened beverages was not simple or straightforward," said Keith Fargo, PhD, of the Alzheimer's Association. "When the researchers controlled for other risk factors, particularly cardiovascular risk factors, it explained most of the association between artificially sweetened beverage intake and the development of dementia. This kind of data does not allow us to say that drinking [these] beverages causes dementia, or that cutting down on artificially sweetened beverages will reduce a person's risk for dementia."
Pase and colleagues analyzed data from the Framingham Heart Study Offspring cohort on people over age 45 years for the stroke arm (N=2,888) and people over age 60 years for the dementia arm (N=1,484). Both groups were primarily Caucasian and were just under 50% male.
Beverage intake was quantified using the Harvard semiquantitative food-frequency questionnaire at three points: cohort examinations five (1991–1995), six (1995–1998), and seven (1998–2001). Participants were then followed for more than 10 years to determine development of stroke or dementia.
Notably, data collection did not distinguish between the types of artificial sweeteners used in the beverages.
Pase and colleagues found that higher recent and cumulative intake of artificially sweetened soft drinks was linked to an increased risk of ischemic stroke, all-cause dementia, and Alzheimer's dementia -- even after adjustment for total caloric intake, diet quality, physical activity, and smoking status.
However, the associations between recent and higher cumulative intake of artificially sweetened soft drinks and dementia were no longer significant after additional adjustment for vascular risk factors and diabetes mellitus.
"Because our study was observational, we are unable to determine whether artificially sweetened soft drink intake increased the risk of incident dementia through diabetes mellitus or whether people with diabetes mellitus were simply more likely to consume diet beverages," Pase said.
Pase noted the findings complement their sister study, published in Alzheimer's & Dementia, that found higher consumption of both sugary and diet beverages was associated with smaller brain volumes, a marker of accelerated brain aging.
Also using data from the Framingham Heart Study Offspring cohort, this study found that people who more frequently consumed sugary beverages, including sodas and fruit juices, were more likely to have poorer memory, smaller overall brain volumes, and smaller hippocampal volumes.
The researchers concluded that their studies highlight a need for more research into this area, especially given how often people drink artificially-sweetened beverages.
In an accompanying editorial in Stroke, Ralph Sacco, MD, of the University of Miami Miller School of Medicine, agreed, writing that the findings "encourage further discussion and more research into this question, for even small causal effects would have tremendous effects on public health due to the popularity of both artificially sweetened soft drinks and sugar sweetened soft drinks consumption. Both sugar-sweetened and artificially sweetened soft drinks may be hard on the brain."
"This kind of research is critical for examining and uncovering public health relationships that may eventually lead to actionable recommendations," added Fargo.
Rachel Johnson, PhD, MPH, RD, past chair of the American Heart Association's Nutrition Committee and professor at the University of Vermont, suggested that people stick to water, low-fat milk, or other beverages without added sweeteners until more data are available: "We know that limiting added sugars is an important strategy to support good nutrition and healthy body weights, and until we know more, people should use artificially sweetened drinks cautiously," she said in a statement.
The researchers acknowledged several study limitations, including the observational nature of the data, the absence of ethnic minorities, and the use of a self-reported questionnaire to obtain dietary intake data, which may be subject to recall bias.
"Even if someone is three times as likely to develop stroke or dementia," Pase said, "it is by no means a certain fate."
Pase reported funding from the National Health and Medical Research Council.
The Framingham Heart Study is supported by the National Heart, Lung, and Blood Institute and by grants from the National Institute on Aging and the National Institute of Neurological Disorders and Stroke.
Sacco received a National Institutes of Health grant for the Northern Manhattan Study. Gardener is also funded by the National Institutes of Health for her work on the Northern Manhattan Study.