THE MULBERRY tree has been immortalized in the nursery rhyme with the refrain, “Here we go round the mulberry bush.”

The mulberry tree also has a crucial role in the silk industry. The silkworm feeds almost exclusively on the leaves of the white mulberry, which is native to East Asia. Several types of mulberry tree exist, usually distinguished by the colour of their edible fruits.

They have the shape of large blackberries, with the black mulberry often used in cooking and making jams. The white mulberry is very light in colour and has a much milder taste.

It has also been the subject of significant medicinal interest in recent times based on traditional usage in Asia as a treatment for diabetes.

The traditional use of mulberry leaves and extracts led to studies finding that blood sugar levels were reduced in some laboratory animals. Further examinations found that mulberry leaves are rich in compounds called iminosugars.

These are chemically similar to sugars, but they prevent the digestion of other complex sugars. One iminosugar is already on the market as an anti-diabetic drug that helps to prevent increases in blood sugar levels after meals. This is a beneficial effect in the prevention and treatment of type 2 diabetes.

As mulberry leaves are rich in naturally occurring iminosugars, they are already available as food-grade teas and powders in Japan and other Asian countries. They are now becoming available as food supplements in Western countries.

A very small number of studies have examined mulberry leaf extracts in humans. One in 2001 found that a small number of type 2 diabetic patients given mulberry leaves showed improvements in blood sugar and lipid levels.

In addition, the changes were significantly better than a control group given the commonly used anti-diabetic drug, glibenclamide.

However, the researchers noted that these were preliminary findings from a small study and much further research was needed to confirm the results.

In addition, the study lasted only 30 days. Since diabetes is a chronic condition, the effects of mulberry over longer periods need to be examined.

A more recent study in Japan found that many commercially available mulberry teas and herbal products contained very small quantities of iminosugars. Some of them contained less than what the researchers estimated as necessary to have any beneficial effect on diabetes.

The researchers then developed an enriched powder which contained about 15 times the iminosugar concentration of many commercial herbal products. When this enriched powder was given to healthy volunteers along with a sugar drink, the normal increase in blood sugar levels did not occur.

Importantly, the blood sugar level did not drop too low despite giving a larger dose. The Japanese researchers are now proceeding with a large clinical study of their enriched mulberry powder.

No adverse effects have been reported in clinical trials of white mulberry leaves. The pharmaceutical iminosugar has led to bloating, gas and diarrhoea in some patients.

Similar problems have not been reported with mulberry supplements, although studies have not given these products to people for an extended period of time.

White mulberry leaves have shown some potential as a helpful food supplement. While much of the research has focused on their iminosugar content, they contain other antioxidants and natural products which may provide additional benefits.

However, very little research has been conducted on these products. Japanese research suggests that many products already on the market contain insufficient iminosugars to produce the benefits found in research studies.

Mulberry supplements may have a role in a plant-based diet, but products with standardised doses are needed. For now, the central focus in preventing and treating diabetes should remain on addressing dietary needs and exercise levels, along with using prescribed medicines when needed. By Donal Omathuna, Irish Times.