Eating leafy green vegetables could offer protection against colds and COVID-19 - Johns Hopkins University study

Basket of leafy green vegetables next to an image of green coronavirus cells
Mum and dad were right - eating your greens does pay off. Photo credit: Getty Images

Eating your five-a-day offers a number of benefits, such as good digestion, a healthy gut and lowered risks of common diseases. And as it turns out, leafy greens may also provide protection against not only common colds, but even COVID-19.

A new study from Johns Hopkins University, a private research university in Baltimore, Maryland, has found that leafy greens such as broccoli, kale and brussel sprouts contain a chemical that may slow the growth of the virus.

The chemical, sulforaphane, is found in cruciferous vegetables, but predominantly in broccoli and kale, autoimmune disease specialist Dr Brooke Goldner told ABC13.

"What it does is it actually cuts the replication of the virus that causes coronavirus in half," Dr Goldner said.

As part of the study, scientists exposed cells to a pure form of sulforaphane two hours before infecting them with COVID-19 and other common viruses. The researchers found the replication of the viruses was reduced by as much as 50 percent - including both the Delta and Omicron variants.

According to the researchers, sulforaphane helps to strengthen the cells' response to an infection, which makes it more difficult for the virus to replicate. The study determined that the chemical can strengthen the immune response against coronaviruses, such as COVID-19 and the common cold.

The best way to benefit from this possible protection is to incorporate more fresh greens into your diet, such as drinking a green smoothie each day, Dr Goldner suggested.

A green smoothie could include adding a handful of kale or spinach to a base of banana, berries and your choice of milk.

Dr Lorraine Jones-Brando, an author of the study and assistant professor of paediatrics at Johns Hopkins University School of Medicine, told local media network WUSA that the chemical is easily accessible if you eat enough cruciferous vegetables.

"We have found that an easily accessible chemical found in cruciferous vegetables, especially in broccoli, helps prevent some of the serious ramifications of infection with coronavirus," Dr Jones-Brando said.

"Sulforaphane has been studied for at least two decades since the early '90s. It has anti-cancer properties, as well as antiviral."

Basket of leafy greens including Brussel sprouts, broccoli and herbs
Leafy greens could offer protection against coronaviruses, according to new research. Photo credit: Getty Images

However, the findings were identified in mice, so more research is needed to determine if eating leafy greens achieves the same effect in humans.

"I wouldn't go and suggest that people take it to prevent COVID-19 right away, but they should take it to be healthier, like as part of a healthy diet of a healthy body and a healthy mind," Dr Alvaro Ordonez, a study author and assistant professor of paediatrics at Johns Hopkins University School of Medicine, told local media.

"Maybe in some time, we'll be able to show that it can help with some of these viral diseases, and then it's just an added benefit."

The amount of sulforaphane expected to be beneficial against coronaviruses is likely achievable as part of a healthy diet, doctors said - so people don't need to add broccoli to breakfast, lunch and dinner in order to gain the benefits. 

"It's about a cup of broccoli heads, or even less of the broccoli sprouts because they have a more concentrated amount," Dr Jones-Brando said.

The researchers reiterated that leafy greens are being investigated as a potential measure to increase an individual's protection against COVID-19, but vaccination, masks and social distancing when appropriate is still the best course of action to shield yourself against the virus.

"It's always a good idea to eat your vegetables," Dr Jones-Brando said.

"Listen to mum, at least on this point."