For anyone who likes their diet soda, a new study may cause you to pause on slurping down your favorite drink.  An analysis of more than 4,000 participants in the Framingham Heart Study Offspring cohort, found that those who drank at least one artificially sweetened beverage a day were almost three times more likely to develop ischemic stroke and 2.9 times more likely to develop Alzheimer’s disease over the course of 10 years than those who drank artificially sweetened beverages less than once a week. 

But before anyone dumps out all of the diet soda, the study authors are cautioning that this study simply showed an association between artificially sweetened drinks and stroke and dementia and not causation.  Association is not the same as causation and other nutrition experts are skeptical of the “controversial but inconclusive” nature of the association.  In addition, it is widely accepted that a person who has high cholesterol, diabetes, and high blood pressure are more likely to develop a stroke or dementia and thus are considered the main drivers for these conditions.  Also the study did not distinguish between the types of artificial sweeteners used in the beverages.  At this time, there is not enough evidence to recommend to people to stop drinking diet sodas.

Food frequency questionnaires used may be unreliable

One problem with this observational study is that it relied on responses to Harvard University’s food frequency questionnaire (FFQ) which ask participants how often and how much of different foods, beverages, and dietary supplements they consume.  When FFQs are used within studies such as this one, their purpose is to assess how a person’s dietary patterns may be associated with certain health outcomes.

But this is where FFQs may not always be the most reliable sources of information.  One is that individuals have a tendency to underreport what they eat and may not always be completely truthful on eating certain foods or they underestimate the amount they are consuming.  Therefore, there could be a substantial amount of bias involved.

However, at the same time, FFQs can be useful.  When observational studies use FFQs this helps to increase a greater body of scientific understanding of a topic.  Yet they cannot be used to establish a cause and effect but instead they can help inform experimental studies such as randomized control trials.  When they are used in this manner, FFQs can lead to scientific advancements in nutrition and food science.

Takeaway message from this study

Even though the headlines from this study may be disturbing and alarming for the millions of Americans who love their daily diet sodas, it is by no means stating they are doomed to develop dementia or ischemic stroke.  But due to the popularity of both artificially sweetened and sugar sweetened soft drinks, it does highlight the need for more research in this area investigating whether or not the frequency of drinking these beverages does indeed increase a person’s risk for these conditions.

At this time, drinking a can or two a day of diet soda is unlikely to be a problem.   From previous research, the artificial sweeteners currently used in these beverages are safe for most people with no credible evidence that they cause risk of diseases such as stroke or dementia.  Many people will switch from regular soda to diet soda to save calories.  However it’s not yet clear how effective it is for preventing obesity and related health problems long term.  In the meantime, it is highly recommended to consider choosing the majority of the time healthier low-calorie beverage choices such as water, skim milk, and unsweetened tea or coffee