A reader asked what are the adverse long-term effects, if any, of consuming the additive contained in Chun Cui He milk tea drink.
The drink was recalled by the Agri-Food and Veterinary Authority because it contained L-theanine, a non-permitted food additive. L-theanine, an amino acid found naturally in tea plants and fungi, is said to have calming properties.
Mind&Body Editor Ng Wan Ching replies:
L-theanine is believed to help relieve stress by inducing a relaxing effect without causing drowsiness and may also have some benefits for the immune system, said doctors.
But information regarding adverse reactions to L-theanine alone (versus when combined with caffeine, as in tea) is lacking.
Clinical trials used small numbers of participants and had poor results, said Dr Timothy Tan, resident physician at the 24-hour emergency department at Raffles Hospital.
One study among elderly participants recorded a higher number of reported headaches among those receiving four doses of L-theanine at 250mg per dose.
In 2006, a study found no consistent, statistically significant treatment-related adverse effects in rats fed high doses of L-theanine for 13 weeks. The areas studied included behaviour, body weight, food consumption and efficiency, and blood and urine analysis.
Large studies in humans have not been undertaken.
There are no reports of clinical toxicity from daily tea consumption. Adverse reactions recorded in human studies using tea extracts include headache, dizziness and gastrointestinal symptoms, said Dr Michael Wong, deputy medical director at Raffles Medical Group.
An increased incidence of renal tubule adenomas in a small number of female rats given high dosages (400mg/kg body weight per day) was attributed to genetic predisposition.
These are a form of kidney tumours that are generally benign or non-cancerous, but carry the potential to become adenocarcinomas which are malignant, said Dr Wong.
There is no consistent and statistical evidence on long-term consumption of L-theanine as there are very limited studies done on this food component, and some have small sample sizes which are not able to yield significant results, said Dr Tan.
However, there are other factors to consider in the long-term consumption of high-sugar-content drinks, which may lead to metabolic problems such as obesity and diabetes, he added.
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