Sutherlandia Safety and Canavanine
by: Dr Nigel Gericke, T.Dr Credo Mutwa, Dr Carl
Albrecht and Prof. Ben-Erik van Wyk.
Sutherlandia is a traditional herbal remedy that
has enjoyed a long history of safe use. The recorded history dates
back to more than 100 years, and the herb has been sold to the public
on a small scale for several decades. Not a single report even suggesting
adverse effects (apart from mild diarrhoea at large overdose) has
ever been recorded.
There has been a recent statement that Sutherlandia
is toxic due to the presence of a chemical called canavanine. There
is no scientific evidence that long term exposure to the very low
amounts of canavanine, found in Sutherlandia frutescens subspecies
microphylla, as sold under the brands of Big Tree, can have any
adverse effects.
Part of the evidence that has been used against
Sutherlandia concerns a historical report of a person who ingested
more than a kilogram of alfalfa seeds (alfalfa is also known as
lucern, “lusern”, Medicago sativa) in a short period in order to
lower blood cholesterol. The person then developed a temporary inhibition
of the production of blood cells (a condition known as pancytopaenia,
that reversed to normal after the extreme overdose was stopped).
It is possible that this condition was caused by the canavanine
in the alfalfa seeds, however, the crux of the matter is that the
daily dose taken by this person contained 1000 times more canavanine
than is found in the daily recommended dose of two 300mg Sutherlandia
tablets. At very high concentrations, canavanine therefore may have
toxic effects, but toxicity due to overdose is also true for even
the most harmless of herbal medicines. Ordinary table salt, taken
in large overdose, can cause high blood pressure or even death.
Alfalfa sprouts are widely sold as a health food
in all over the world, despite the fact that alfalfa contains more
canavanine than Sutherlandia. Even a modest daily portion of alfalfa
sprouts would contain substantially more canavanine than the amount
present in a recomended daily dose of Sutherlandia. Despite the
presence of canavanine in alfalfa, the Food and Drug Administration
of the United States (FDA) has placed alfalfa in the category of
food “generally regarded as safe”, so-called “GRAS” status. If the
statement is correct that daily ingestion of small amounts of canavanine
is harmful, one would have expected that this would have become
evident from the millions of people all over the world eating alfalfa
sprouts. Clearly this is not the case.
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