Milling grain strips out vitamin B1, so 59 countries put it back
Thiamine, vitamin B1, is a bitter, oddly smelly white powder that your cells cannot run without: it helps turn sugar into usable energy and helps nerves build myelin. Refining grain removes much of it, which is why dozens of countries now require flour, rice or maize to be fortified.
In the body thiamine is converted into several phosphate forms. The best understood, thiamine pyrophosphate, is a coenzyme for enzymes that shift two-carbon units around. One of them, pyruvate dehydrogenase, bridges glycolysis and the citric acid cycle; another catalyses a rate-limiting step in that cycle. Together they feed the production of ATP, the cell's energy currency, and in the nervous system pyruvate dehydrogenase also helps make myelin and the neurotransmitter acetylcholine. Some cousins remain puzzling: one derivative sits in small amounts in vertebrate liver with no known job.
Shortage causes a string of disorders, most famously beriberi and Wernicke encephalopathy, and its early warnings include confusion, irritability, weight loss and a general sense of feeling unwell. In Western countries chronic heavy drinking is a recognised risk, as are older age, diabetes and bariatric surgery. A study of 286 hospitalised US veterans without alcohol problems found about a quarter had low plasma thiamine, suggesting deficiency is easily overlooked even where food is plentiful.
Lentils, peas, whole grains, pork and nuts all supply it. US reference intakes set in 1998 put the recommended daily amount at 1.1 mg for women and 1.2 mg for men aged 14 and over. By February 2022, 59 nations, the majority in northern and sub-Saharan Africa, required fortification of wheat, rice or maize, and 18 more ran voluntary schemes. No upper intake limit has been set, because there is no human evidence of harm from high doses, though rare reactions have followed injections.
Humans cannot make it, but archaea, bacteria, plants and fungi can, assembling two ring structures separately and joining them. Their production is controlled by a riboswitch: when thiamine is plentiful it binds the relevant messenger RNA and halts enzyme synthesis. That TPP riboswitch is the only one known in both simple and complex cells. Chemists first synthesised the vitamin in 1936.
Source: Thiamine
