Prof Randall Merchant, professor of Neurosurgery and Anatomy at Virginia Commonwealth University, in the US, has been involved in research into brain tumours, traumatic brain injury, and stroke. In 1986, he began clinical trials into whether Chlorella might boost a patient's immune system.

"Fascinating," is how he describes the results. "It didn't make brain tumours go away or shrink, so it didn't cure the cancer, but it did help the patients by boosting their immune system so that they resisted opportunistic infections."

Since then, Prof Merchant has performed clinical trials to test whether chlorella could be useful in helping with chronic conditions such as fibromyalgia, ulcerative colitis and hypertension. In the first two trials, his team found that "patients' symptoms diminished quite nicely". For hypertension, the results were more dramatic; while it lowered blood pressure in about 50 per cent of cases, which was promising, the studies showed that it also significantly lowered serum cholesterol.

In 2008, he examined the effects chlorella has on those with metabolic syndrome – the collection of symptoms that often lead to the cells in our bodies becoming less sensitive to insulin, and therefore a precursor to diabetes.

Prof Merchant says: "It seems that chlorella turns on the genes that control the way insulin is normally used by the cells in the body. This research shows that chlorella could in theory help correct the problems of metabolic syndrome. It is not a magic bullet, but taking it is one other preventive thing you can do, like exercise or watching your diet."