Published: January 6, 2023

Last Updated: January 9, 2023 Ruairi J Mackenzie

A new study suggests that aspartame, the common sweetener, produces anxiety-like behavior in mice, an effect that was passed on to multiple subsequent generations.

The research was conducted by a team at the Florida State University College of Medicine and led by Pradeep Bhide, the Jim and Betty Ann Rodgers Eminent Scholar Chair of Developmental Neuroscience in the Department of Biomedical Sciences. Bhide's lab focuses on the field of epigenetics, which explores how the environment can alter how genetic material is read. “Our lab has been interested in examining how environmental exposures influence traits (behavioral, cellular, molecular, etc.) not only in directly exposed individuals but also in their un-exposed descendants. This research falls into a field of biology that examines heritable effects of environmental exposures, often ancestral exposures,” Bhide told Technology Networks.

From nicotine to sweeteners

Bhide’s lab has spent years exploring epigenetic inheritance. In a 2018 study, they looked at the effect of exposing male mice to nicotine, noting behavioral changes to the exposed mice’s offspring (called the F1 generation) and their offspring’s offspring (called the F2 generation). In their paper, the team pointed out that while smoking during pregnancy is strongly advised against due to potential impacts on the fetus, less is known about how male nicotine exposure may affect the next generation through modulation of sperm cell DNA. They subsequently detailed the effects of exposure to another regularly consumed compound, this time one considered safe for human consumption, the sweetener saccharin. Again, the team was able to trace an intergenerational effect profile. The focus of Bhide's next work was an even more common sweetener, aspartame.

The team first decided to study how exposure to the sweetener affected anxiety behaviors, a common focus of behavioral research. “There were other reports in the scientific literature showing that aspartame produced anxiety in experimental animal models, but the reports could not reach a consensus,” says Bhide. Their data in the exposed mice showed an effect in both males and females. But it was their findings in the following generations that were most novel and surprising, says Bhide.

The team evaluated anxiety using standard behavioral tests. Mice, which are prey animals, will hug the edges of an open space when they feel anxious. The F1 and F2 offspring of aspartame-exposed mice were noted to spend significantly less time in the center in an open-field test, suggesting heightened fear and stress. 

Diazepam details

The next step for Bhide’s team was to try and ascertain how aspartame might be inducing anxiety. They injected the fearful mice with either saline or 3 mg/kg of the benzodiazepine compound diazepam – a dose calculated to avoid impairing the mice’s movement through sedation. Diazepam is a drug commonly used to treat anxiety or panic disorder in humans, and dosed mice spent significantly more time in the center of the open field test, suggesting that their anxiety had reduced.

This finding alone gave Bhide a hint as to the source of the aspartame-induced anxiety. “Since diazepam alleviated the anxiety, a GABAA receptor-mediated mechanism is highly likely to be the cause of the anxiety. Specifically, downregulation of GABAA receptor signaling in brain circuits associated with anxiety is believed to be the cause,” he comments.

This assertion is backed up with data the team generated using RNA sequencing. This enabled them to explore how gene expression was altered in the brains of mice given diazepam – in particular focusing on the amygdala, a region tightly linked to fear and emotion. In these areas, Bhide’s team found that aspartame produced gene expression changes, reducing GABA signaling and increasing excitatory glutamate signaling. “We believe that aspartame produces a shift in the excitation-inhibition balance, in favor of excitation,” he says.

The specifics that underlie this more general mechanism remain hazy. Aspartame, says Bhide, is broken down into aspartic acid, phenylalanine and methanol in the intestines. The first two compounds are potentially neuroactive, but further analysis will be required to evaluate their respective contributions to any anxiety-provoking effect.

The human question

If you are reading this over a cup of heavily sweetened coffee, you’d be forgiven for throwing your mug out the nearest window. “Obviously, our study raises significant concerns about consuming aspartame-containing food products or drinks. It would be prudent to be aware of these concerns based on our findings,” says Bhide. The idea that your morning caffeine fix might have impacts on your children and grandchildren is particularly concerning, but some digging into the study’s data provides some respite. Let’s take a closer look.

The first factor to consider is that the effects were only noted in mice, which are decidedly not humans. While Bhide’s team chose a dose that was indicative of average aspartame consumption in people, the same effects may not be observed in humans – we just don’t know yet. Further, the effects were notably attenuated in the F2 generation. After multiple comparisons analysis, a step taken to weed out potentially weak statistical findings, most of the effects of aspartame on RNA sequencing disappeared, even if the behavioral effects were maintained, suggesting some gradual attenuation through generational inheritance.

There is also a significant difference between a temporary and enduring epigenetic effect. The team bred their aspartame-exposed mice during the dosing process. Could it be possible that after a period of non-exposure, the effect of aspartame could be reduced? “We are asked this question often, and will examine it in future studies,” notes Bhide.

The team’s next work is already underway – looking at the effects that aspartame has on learning and memory in exposed males and descendants, and potential epigenetic changes in both the brain and sperm cells. Aspartame, nicotine and saccharin are just a handful of the vast number of environmental factors that can likely change our epigenetic makeup. How significant these effects are in humans, and whether they are large enough to warrant potential fathers weaning themselves off sweeteners prior to baby-making remain open questions. But labs like Bhide’s are on the case. “It is a hot area of research in experimental and evolutionary biology today, and our research is part of this endeavor,” Bhide concludes.

In an email to Technology Networks, the International Sweeteners Association, an international non-profit body representing sweetener suppliers, shared the following statement responding to the study. “Responding to a new animal study by Jones et al., the International Sweeteners Association (ISA) would point to the safety of the low/no calorie sweetener aspartame, repeatedly confirmed by food safety authorities worldwide.

Indeed, prior to being approved for use on the market, aspartame has undergone stringent safety assessments by food safety bodies worldwide including the Joint Expert Committee on Food Additives of the United Nations Food and Agriculture Organization (FAO) and of the World Health Organization (WHO), the European Food Safety Authority (EFSA), and the US Food and Drug Administration (FDA).

Specifically, in 2013 EFSA carried out the most comprehensive risk assessment of aspartame ever undertaken. Based on the extensive scientific evaluation of all available data, including data relating to potential toxicity and genotoxicity, EFSA ruled out any potential risk and reconfirmed that aspartame is safe.6

It is also important to highlight that the results from the study by Jones et al. performed on mice cannot be extrapolated to humans. A study funded by the UK Food Standards Agency in 2015, which examined anecdotal evidence of perceived effects of consuming aspartame, including anxiety, concluded that “there was no evidence of any acute adverse responses to aspartame”. As stated by the authors of the study, “This independent study gives reassurance to both regulatory bodies and the public that acute ingestion of aspartame does not have any detectable psychological or metabolic effects in humans.” [Updated, January 09, 2023] 

Reference: Jones SK, McCarthy DM, Vied C, Stanwood GD, Schatschneider C, Bhide PG. Transgenerational transmission of aspartame-induced anxiety and changes in glutamate-GABA signaling and gene expression in the amygdala. Proc. Natl. Acad. Sci. 2022;119(49):e2213120119. doi: 10.1073/pnas.2213120119

This article was updated on January 09, 2023 to include comment from the International Sweeteners Association.