From algorithmic efficiency to cascading health burdens: a text-mining study of online food delivery riders in the platform economy.

Mental disorders contributed significantly to the global burden of disease, with 125.3 million years lived with disability (YLDs) attributed to mental disorders in 2019, the second largest cause of YLDs worldwide. Some nutrients and diets are considered modifiable risk factors for mental health. Alanine, a non-essential amino acid, is usually found in meat. Alanine supplements are popular in sports nutrition due to their ability to enhance athletic performance and exercise endurance. The potential role of alanine in mental disorders has raised concern, considering that it can cross the blood–brain barrier and may alter the levels of neurotransmitters or provide energy for the brain. In mammals, alanine plays a key role in the glucose-alanine cycle, which is a provider of energy to the muscle, nervous system, and brain. It is also a precursor of several substances, including glutamate, glutamine, -alanine, and -aminobutyric acid (GABA), which are involved in neurotransmission and the metabolism of amino acids in the central nervous system. Importantly, alanine may also act as an agonist that binds to the brain glycine site of -methyl-d-aspartate (NMDA) receptors (ionotropic glutamatergic receptors). Dysfunction of NMDA receptors is known to be associated with various psychiatric disorders, including depression, bipolar disorder, schizophrenia, and anxiety. However, it remains unclear whether alanine is a friend or foe in mental health. In animal experiments, central injection and oral administration of alanine showed an attenuating effect on anxiety. A small placebo-controlled trial found that oral administration of d-alanine improved the negative, positive, and cognitive symptoms of patients with schizophrenia, suggesting a therapeutic role for alanine in psychosis. A later study measured plasma alanine levels in patients with schizophrenia and found that from admission to discharge, patients’ total plasma alanine increased significantly with improvement in clinical symptoms, adding to the evidence for a beneficial effect of alanine. However, contradictory evidence showed that plasma alanine was higher in patients with bipolar disorder compared with controls and positively correlated with the severity of depression, raising safety concerns. Also, an in vitro study showed that children with attention-deficit hyperactivity disorder (ADHD) had an elevated access of alanine in the brain which may interfere the normal brain activity, but epidemiological studies are lacking. It is worth noting that most studies had relatively small sample sizes or were conducted in animal models. Observational studies are vulnerable to confounding by factors such as socioeconomic status, lifestyle, and medication. They may also lack sufficient power for rare outcomes. Large randomised controlled trials (RCTs) designed to assess the mental health effects of alanine may be challenging due to ethical issues and funding constraints. Mendelian randomisation (MR) offers a promising method for studying the causal effects of alanine without the need for harmful interventions. MR studies use genetic variants as instruments to predict exposure, independent of environmental factors, as genetic variants are determined at conception, which largely mitigates confounding, a major limitation of traditional observational studies. The increasing availability of large genome-wide association studies (GWASs) has enabled well-powered MR studies.