Thiamine (vitamin B1): deficiency, alcohol and supplements

Thiamine is a cofactor in enzymes that release energy from glucose. The NHS describes it as helping the body break down and release energy from food and keeping the nervous system healthy. MedlinePlus adds that it supports muscle contraction and nerve signalling.

The brain and heart burn a lot of glucose and cannot easily switch to other fuels, so they feel the consequences first when thiamine runs short.

According to the NHS, good sources include peas, fresh fruit such as bananas and oranges, nuts, wholegrain bread, fortified breakfast cereals and liver. MedlinePlus adds pork, beef, trout, tuna, eggs, legumes and seeds. Refined white flour and polished rice lose much of their thiamine in milling, which is why many countries fortify flour.

The NHS notes that pregnant women should avoid liver because of its vitamin A content, so other sources are preferable then.

Alcohol misuse is the main route in the UK. Alcohol reduces thiamine absorption, increases its loss and is often accompanied by a poor diet. Other risks include prolonged vomiting such as in hyperemesis gravidarum, long periods of poor intake in eating disorders or severe illness, bariatric surgery, dialysis, some diuretic use and cancer-related malnutrition.

Beriberi, the classic deficiency disease, can affect the heart and nerves. In developed countries a neurological presentation is more likely, and clinicians keep a low threshold for treating anyone at risk.

Wernicke encephalopathy is an acute brain disorder from thiamine deficiency. The textbook triad is confusion, unsteadiness of walking and abnormal eye movements, but a trial paper notes that up to 90 percent of cases do not show the full triad, so doctors treat on suspicion. If untreated it can progress to Korsakoff syndrome, an enduring memory disorder.

Treatment uses thiamine given by injection or drip. The same paper explains why: no more than 4.5mg is absorbed from oral doses above 30mg, and observational studies suggest parenteral thiamine sharply reduces deaths. The best dose and duration are still debated, and the randomised trial in that paper found no significant differences between several regimens on cognition or neurological function.

Anyone with sudden confusion, double vision or loss of balance, particularly with a history of heavy drinking or severe vomiting, should be taken to A&E or 999 called.

People without risk factors rarely need extra thiamine. Where a clinician recommends it, for example during alcohol detoxification or after bariatric surgery, the product and dose are tailored. The NHS regards 100mg or less a day as unlikely to cause harm, and MedlinePlus states there is no known poisoning from excess intake, although very large injected doses are an inpatient matter.

• Include a thiamine source such as wholegrain bread or fortified cereal each day.

• If you drink heavily, seek help from your GP or a local alcohol service before stopping suddenly, because withdrawal needs supervision.

• After weight-loss surgery, take the multivitamin plan your surgical team gives you.

Whole-blood thiamine or red-cell transketolase tests exist but are not used to delay treatment of suspected Wernicke encephalopathy. For routine screening in malabsorption the test may be requested alongside other vitamin levels.