Some studies link aspartame with cancer risk, but the evidence is inconsistent. For example, some observational studies show an association between greater aspartame intake and increased cancer risk,[2] whereas others do not.[3] While observational studies can help evaluate the likelihood that a substance — a food additive, nutrient, pollutant, etc. — is involved in disease risk, they cannot prove causality. Observational studies also rely heavily on self-reported dietary intake data, which introduces recall bias. Other types of studies — cell experiments, animal studies, and randomized controlled trials — can help evaluate whether a substance causes a disease. Regulatory bodies then evaluate the strength of all known evidence to determine whether a substance can theoretically cause disease in humans.
Accordingly, regulatory bodies such as the International Agency for Research on Cancer (IARC) and the Joint Food and Agriculture Organization and World Health Organisation Expert Committee on Food Additives (JECFA) have concluded that aspartame is “possibly carcinogenic” to humans — i.e., there is limited, but not convincing, evidence for aspartame causing cancer in humans and less than sufficient evidence for aspartame causing cancer in experimental animals.[4] Accordingly, food regulatory bodies including the US Food and Drug Administration (FDA) and the European Food Safety Authority (EFSA), which determine whether foods (and additives) are safe to eat, currently conclude that aspartame is safe for human consumption at current exposure levels.[5] That said, given that some evidence suggests potential adverse effects, regulatory bodies also conclude that further high-quality studies are needed.
So, in the amounts people are likely to consume, aspartame is unlikely to pose a major risk. However, if people want to reduce their exposure to any potential hazard that might be posed by aspartame, they can choose to avoid foods containing aspartame. For more information, read Does aspartame cause cancer in humans?.