Mushroom high: Why we can’t get enough of the ‘sunny sponges’

For many, they are slimy and unappetising, but Clare Finney finds out why you should be making more room in your fridge for these earthy fungi

Sales are outstripping those of every other vegetable (iStock)

There is an evocative and eerily brilliant poem by Sylvia Plath describing the growth of mushrooms: how their “Soft fists insist on/ Heaving the needles”. “We shall by morning/ Inherit the earth”, it concludes. How prescient it has proved.  

Fast forward from 1959 to 2020 and sales of mushrooms are outstripping those of every other vegetable, as people grasp at anything and everything that might increase their capacity to resist and recover from Covid 19. In the case of mushrooms – sales of which are up 18 per cent in Sainsbury’s and 10 per cent in Tesco – this impulse is not entirely unfounded: mushrooms are a good source of vitamin D, and though its primary role is in bone and muscle health there have been reports that the vitamin can play a role in resistance to this virus. 

There is not enough evidence, UK health bodies NICE and NHS believe, to determine a causal relationship between the vitamin and the virus, but what is indisputable is that thanks to lockdowns and self-isolation, many of us have been spending more time indoors than ever before; and that this will have an impact on our body’s ability to manufacture what is known as “the sunshine vitamin”, on account of the sunshine’s ability to stimulate vitamin D production in the skin.  

Those who are shielding, who are particularly vulnerable to the virus, are entitled to vitamin D supplements on the NHS. Yet as the nights, and the prospect of stricter tiers and lockdowns, have closed in on us, those who aren’t entitled to supplements have sought to up their own intake through their diet – which is where the soft, deceptively meek mushrooms have come in.  

The  UK & Ireland Mushroom Producers, a partnership between key mushroom farmers across the region, describes them as “sunny sponges”. “Much like our skin, they transform ultraviolet light from the sun into the vitamin D and continue to do so even after they have been harvested,” says a representative. “They are the only vegetarian food that can make vitamin D as they contain a specific compound called ergosterol which is converted into vitamin D when exposed to the sun’s ultraviolet (UV) rays.” For many mushrooms you find in the shops, this isn’t relevant: they’re grown indoors, so don’t have the opportunity to create the sunshine vitamin. 

Farmers often call mushrooms ‘sunny sponges’ as they continue to transform sunlight into vitamin D even after they have been harvested (iStock)

In recent years, however, mushroom producers have started selling vitamin D-enriched mushrooms: that is, ones that have been exposed to UV light – to the point where eating just eight a day would provide your daily amount of the vitamin as recommended internationally. The catch? There is a difference between the type of vitamin D mushrooms create and the type of vitamin D generated by our skin in response to sunlight, and which can be found in our bodies and animal products – particularly eggs and oily fish.  

“For vitamin D to be most effective, it has to be vitamin d3 – and we need sunlight or animal products to create that,” says BDA-accredeited consultant dietitian Linia Patel. Vitamin d2 isn’t wasted on us – but it takes much longer to metabolise it into something that the body can use. “Even if you are eating mushrooms you still need to follow the guidance of Public Health England and take supplements,” says Patel – on the fair assumption that very few of us are getting sufficient sunlight. Indeed, research suggests that one in five Britons are deficient in the vitamin – a figure which surges in winter months, even before you factor in lockdowns. Which is why come January more than 2.5 million people in England are to be offered a free supply of vitamin D.

It’s good news that we’re eating more mushrooms, they’re good for us and are better for the planet too (iStock)

“The government is taking action to ensure vulnerable individuals can access a free supply to last them through the darker winter months. This will support their general health, keep their bones and muscles healthy and, crucially, reduce the pressure on our NHS,” said health secretary Matt Hancock, who has instructed NICE and the NHS to look once more into possibility of there being a direct link between immune response to coronavirus and vitamin D. The grounds for this are complex, says Linia – “immunity is very complex, there’s no one solution” – but some clinical trials do suggest that a substance called betaglucanes “works indirectly to improve gut health. It is the substance that makes mushroom slimy – but it’s high in soluble fibre, and soluble fibre is what bacteria in our gut like to eat.”  

There are certainly strong links between a happy gut and immunity, and between vitamin D and immunity – but research investigating the link between vitamin D and Covid-19 protection is ongoing and as yet inconclusive. In short, there is more to the extraordinary surge in mushrooms sales than gut health, or even vitamin D. “Mushrooms’ sustainable and versatile nature make them the perfect choice for shoppers following a flexitarian or plant-based diet,” says Noel Hegarty, UK & Ireland Mushroom Producers MD. They have a meaty texture, and an umami taste profile. They can stand in for beef in wellingtons and burgers. “This doesn’t make them a meat replacement,” stresses Patel: just because something feels and even tastes like meat doesn’t mean it has anything like the same level of protein or other nutrients contained within meat. “Those opting for a mushroom burger should still take care to opt for a “seeded burger bun, some pesto – otherwise you aren’t getting the nutrients you need.”  

It is interesting that one of properties that make mushrooms so good for us – their slimy texture –   is also what puts many people off them. The chief benefit of lockdown – beyond the obvious reduction in Covid infections – has been in people cooking more, or in some instances cooking for the first time. Done well, mushrooms needn’t be slimy: they are in fact incredibly versatile, and their texture easily countered by being blitzed into soups or sauces. Perhaps more time spent in the kitchen has helped people explore the potential of these tasty spores.  

In any case, and regardless of any conclusive outcome regarding vitamin D and Covid 19, it’s good news that we’re eating more mushrooms. They’re good for us and, with a relatively small environmental footprint comparative to other crops, they are better for the planet. They may not inherit the earth by morning, but it is no bad thing if they do.