A team of international researchers have identified an important association between the outcome of COVID-19 and regional selenium status in China.
Led by Professor of Nutritional Medicine at the University of Surrey, Margaret Rayman, the project was prompted by earlier research revealing disparity in selenium levels in China.
A belt of selenium deficiency runs from the northeast to southwest in the country, where populations have recorded the lowest and highest selenium status in the world.
How much selenium is consumed by populations depends on the environment in which the crops and plants they eat (or indeed, the livestock eat) are grown, Rayman explained.
“It relates to gross differences in geology underlying the soil and to other factors like soil acidity, organic matter content soil bacteria etc. that affect the amount of selenium that is taken up into the plants,” she told FoodNavigator.
“Not only do we eat the plants, but they are used as animal forage so also affect the levels in meat and poultry.”
Selenium’s key dietary sources
Selenium is an essential trace element recognised for wide-ranging effects, including antioxidant and anti-inflammatory effects.
In contrast to many other micronutrients, it is also known to be a toxic element. When consumed in high concentrations, it can cause garlic breath, hair and nail loss, disorders of the nervous system and skin, poor dental health, and paralysis.
“Fish and seafood are good sources, somewhat higher than meat and poultry,” Rayman told this publication.
Cereals, on the other hand, are very variable, she continued. In North America, bread and cereals are good sources. In Canadian wheat, for example, selenium content are ‘quite high’ – certainly higher than the UK and Europe.
“However, because we eat a lot of them, they do make quite a good contribution to total selenium intake even in the UK and Europe.”
Brazil nuts are another high source, she continued, however it is possible to overdose on them. Some may have very high levels of selenium, yet the problem is, they are ‘very variable’.
Concerning geographical regions, selenium status – as measured by plasma or serum selenium – varies by country and corresponds to intake.
Intakes are high in Canada, the US, Japan, and Venezuela, yet much lower in Europe, and in particular, Eastern Europe. New Zealand’s selenium status, which was relatively low, has increased since the importation of high-selenium Australian wheat.
And as previously mentioned, China has areas of both selenium deficiency and excess.
Linking selenium levels with COVID-19 recovery in China
The researchers undertook a population-based, retrospective analysis using real-time data collection from Chinese, nongovernmental website Baidu. The site provides daily updates on COVID-10 confirmed cases, numbers cured, and numbers who died in each province, municipality or city.
Rayman’s team compared this data with city population selenium status data, gleaned from earlier hair samples.
Analysing data from 18 February 2020, the researchers noted that the cure rate inside Hubei Province, of which Wuhan is the capital, was ‘significantly lower’ than in all other provinces in China combined.
The death rate inside Hubei Province was significantly higher than the death in other Chinese provinces.
Results revealed an association between the reported cure rates for COVID-19 and selenium status.
In Hubei’s Enshi city, for example, the cure rate was 36.4% higher than in other Hubei cities, where the cure rate was 13.1%. Enshi is known for its high selenium intake and status, compared to typical levels in Hubei. “So much so that selenium toxicity was observed there in the 1960s,” noted the researchers.
Elsewhere, Heilongjian Province, outside of Hubei in northeast China, is a notoriously low selenium region. Heilongjian had a much higher death rate, at 2.4% higher than that of other provinces.
The researchers acknowledged certain limitations in the study, not least that the association between hair selenium and COVID-19 cure rate was based on city population selenium status data dating mostly from 2011 – and in some cases, earlier.
Further, city or patient-level data could not be collected for certain likely confounders, including diabetes, chronic respiratory disease, and hypertention.
“We are fully aware, therefore, that the association shown is far from being robust to criticisms of confounding. At best, it points towards the need for further research, particularly when viewed in the context of associations between selenium status and disease outcome found with other viruses,” they noted.
“In due course, more individual-level data will emerge, and the association between the severity of COVID-19 and many factors, including selenium, can be explored.”
What could these findings mean for others around the globe?
So what are the implications of these findings for global populations amid the coronavirus pandemic? Do we ingest enough dietary selenium in our day-to-day lives?
According to Rayman, some people will certainly already have enough selenium in their diet, if they consume cereals, bread, meat, poultry, fish, and particularly seafood.
For those living in North America, Venezuela, Japan, and some parts of Australia, the Professor predicts diets will be sufficient in selenium. Vegan and vegetarians, however, will have a lower intake of selenium, as they will not be eating fish, meat or poultry, she continued.
Selenium can also be taken as a dietary supplement. “If going for a supplement, I would recommend a multi-vitamin and mineral supplement which will not have too much selenium,” Rayman advised.
“A daily intake of 60 microgrammes for women and 75 micrograms for men is the recommended UK intake (Reference Nutrient Intake) whereas it is 55 micrograms/d in the US (RDA).
“It is important to realise that selenium can be toxic if too much is consumed.”
Source: American Journal of Clinical Nutrition
‘Association between regional selenium status and reported outcome of COVID-19 cases in China’
Published: 28 April 2020
Authors : Jinsong Zhang, Ethan Will Taylor, Kate Bennett, Ramy Saad, Margaret P Rayman
Source: The Lancet
‘Selenium and human health’
Published online 29 February 2012
Author: Margaret P Raiman