Adapted from Optimum Nutrition Summer 2020

Feature

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Studies have found that low levels of selenium could be linked with severity of COVID-19. But what is selenium and why do we need it?

Selenium (Se) is an element found in Brazil nuts, seafood, fish, organ meats, meat, poultry and grains. Brazil nuts are very high in selenium (about 544 mcg per 28 g). This means that just two Brazil nuts can contain more than a day’s recommended intake.

Selenium has critical roles in reproduction, thyroid hormone metabolism, DNA synthesis, and protection from oxidative damage and infection. Selenium deficiency produces biochemical changes that may predispose people who experience additional stresses to develop certain illnesses. Keshan disease (congestive cardiomyopathy which historically occurred in parts of China) is an example, resulting from selenium deficiency and Coxsackievirus infection.

Selenium deficiency and COVID-19

According to a team of international researchers, being deficient in selenium could negatively affect a patient’s recovery from COVID-19.

Led by Professor Margaret Rayman from the Department of Nutritional Sciences, the University of Surrey, scientists analysed data of COVID-19 incidence (up until 18 February) from Chinese provinces and municipalities with more than 200 cases, and from Chinese cities with more than 40 cases.

They found that in areas with high levels of selenium, people were more likely to recover from the virus. In the city of Enshi in Hubei Province, for example, which has the highest selenium intake in China, the cure rate (percentage of COVID-19 patients declared ‘cured’) was almost three times higher than the average for all the other cities in Hubei Province.

By contrast, in Heilongjiang Province, where selenium intake is among the lowest in the world, the death rate from COVID-19 was almost five times as high as the average of all the other provinces outside of Hubei.1

The team reported that the COVID-19 cure rate was also significantly associated with selenium status (as measured by levels of selenium in hair) in 17 cities outside of Hubei.

Rayman said: “Given the history of viral infections associated with selenium deficiency, we wondered whether the appearance of COVID-19 in China could possibly be linked to the belt of selenium deficiency that runs from the north-east to the south-west of the country.”

However, the team acknowledged that there are many confounding factors such as age, underlying health status and lifestyle that they were unable to take into consideration.

Kate Bennett, a medical statistician at the University of Surrey, said: “There is a significant link between selenium status and COVID-19 cure rate, however it is important not to overstate this finding; we have not been able to work with individual level data and have not been able to take account of other possible factors such as age and underlying disease.” 

How much selenium do you need?

Despite the importance of selenium, however, it is possible to take in too much — especially if taking supplements. The NHS states that although selenium helps the immune system to work properly, helping to prevent damage to cells and tissues, taking in too much can cause a condition called selenosis which, in its mildest form, can lead to loss of hair, skin and nails.

Professor Rayman cautioned against taking supplements unnecessarily. “Be careful because too much selenium is as dangerous as too little,” she said. “People who eat fish/seafood, meat and poultry in the UK are probably getting a reasonable amount. If they are vegetarian or vegan, this will not be the case. In those cases, a multivitamin and mineral supplement would be a safe option. Recommended [selenium] intake (total, food + supplements) is 75 mcg/d for men and 60 mcg/d for women, or by the US RDA, 55 mcg/d. We get on average about 35-40 mcg from food in the UK.”

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