How Aloe vera became a cure-all and cosmetic superstar

26 Jul

https://www.newscientist.com/article/mg22730301-200-how-aloe-vera-became-a-cure-all-and-cosmetic-superstar/
15 July 2015

Stephanie Pain is a consultant for New Scientist

Its mucilaginous gel is big business and used daily by many, but
until now we had no idea where Aloe vera came from or what makes it
so special

IF YOU are looking for a celebrity to endorse a beauty product, they
don’t come much bigger than Cleopatra. The Egyptian queen’s beauty
regime famously included bathing in asses’ milk. But that was
probably propaganda put about by her Roman enemies. So what to make
of another legend? Cleopatra, the woman who seduced not one but two
great Roman leaders, enhanced her charms with a skin-softening gel
scooped from inside the succulent leaves of the plant we know as
Aloe vera. If true, then she was an early fan of a natural product
now worth an estimated $13 billion a year.

Today, the mucilaginous gel has an extraordinary range of uses – as
a herbal remedy for ailments ranging from skin diseases and burns to
digestive troubles, and as a soothing balm in cosmetics and
toiletries, from suntan lotion and antiperspirant to detergent and
even toilet paper. Increasingly, powdered gel is added as a
health-boosting supplement to foods such as yogurt. It is one of the
most widely used natural products in the West.

You might think that there’s little left to learn about such a
familiar plant. You couldn’t be more wrong. For a start, nobody
knows where it originally came from. Aloe vera has been cultivated
in most warm parts of the world for so long that people often
believe it has always grown there. But a truly wild population has
never been found and the plant is presumed extinct in its ancestral
home.

Even more of a puzzle is why Aloe vera dominates trade so completely
when there are more than 500 other species of aloes, many with
equally succulent gel-filled leaves. What’s so special about this
particular plant? Botanists have turned detective to solve these
mysteries.

Historical documents provide some clues. The first reliable record
of Aloe vera as a medicine dates from around 65 AD – a century after
Cleopatra’s death – when the Greek surgeon Dioscorides wrote De
Materia Medica, detailing his accumulated knowledge of medicinal
plants. In it, he clearly describes Aloe vera, alongside an accurate
illustration. Dioscorides travelled with Emperor Nero’s army and
used his favourite healing plant to treat all manner of soldiers’
problems – to soothe sore throats and ulcerated genitals, and get
rid of boils and piles. He described, too, how he beat the leaves to
a pulp and laid them on wounds to stop bleeding.

By Dioscorides’ day, the “healing plant” was already widely
cultivated around the Mediterranean and beyond. You need to dig much
further back in time to discover the origins of Aloe vera’s
phenomenal success. “The use of Aloe vera gel probably began
centuries or possibly millennia before Dioscorides took it with him
on his army campaigns,” says Olwen Grace of London’s Royal Botanic
Gardens at Kew. There are ancient references to what might have been
Aloe vera, but it is hard to be certain when all you have is a name
in an ancient script, a rough painting on the wall of a tomb or a
list of ingredients in a prescription on a papyrus. So Grace decided
to tackle the problem another way – by delving into the evolutionary
history of Aloe vera and its many relatives.

In a mammoth project to reconstruct the aloe family tree, Grace and
her colleague Nina Rønsted, a specialist in the evolution of
medicinal plants at the Natural History Museum of Denmark in
Copenhagen, teamed up with botanists in Africa and Europe. Together
they amassed DNA from nearly 200 aloes from all over their
geographical range. By comparing key DNA sequences, the team built a
near complete picture of how the hundreds of aloes living today are
related, how they evolved and when and where they originated.

The first aloes appeared in southern Africa around 19 million years
ago and began to diversify as the subtropical climate started to
become more seasonally hot and dry. Struggling to adapt to changing
conditions in the far south, they spread north-eastwards until they
reached the Horn of Africa. Then, around 5 million years ago, a few
dispersed north to the Arabian peninsula, west across central Africa
and east to Madagascar, setting the scene for a rapid burst of
evolution in a rich variety of new habitats.

Among those that appeared on the Arabian peninsula is a group of
seven species that share many features with Aloe vera. Sure enough,
a comparison of their DNA showed that these are its closest
relatives (BMC Evolutionary Biology, vol 15, p 29). “So we now know
that Aloe vera originated somewhere on the Arabian peninsula,” says
Grace. “That gives us a starting point in the search for the
beginnings of the Aloe vera phenomenon.”

As well as pinpointing the plant’s ancestral home, the pair expected
to find an evolutionary explanation for its huge success (see
“Mysterious healing powers”). Around 25 per cent of aloe species
have some medicinal use, but these are often known only locally, and
the few that are traded are small beer in comparison with Aloe vera.
So what makes Aloe vera gel special? The answer was a surprise.

Accidental hero

A preliminary screening of 30 aloe species indicated that,
chemically, there was little to distinguish Aloe vera gel from the
others (Phytochemistry, vol 93, p 79). The family tree revealed why.
“It’s not a unique lineage so there’s no reason to think Aloe vera
has unique chemical properties that might explain its popularity,”
says Rønsted. In fact, looking at the family tree, the 120 or so
aloes known to have some medicinal use come from many different
branches. They don’t share close genetic links but they do share
some features: they have large succulent leaves with firm gel, short
stems that make leaves easy to harvest and they are easy to grow.
People seem to have chosen them for pragmatic reasons, rather than
for their chemical properties.

The new evidence suggests Aloe vera’s commercial success was an
accident of human history. In ancient times, the southern Arabian
peninsula was a key trading hub (see map). One of the region’s most
sought-after products was incense, particularly frankincense and
myrrh – resins tapped from local trees. By the 4th century BC, the
incense trade was flourishing and there was an established route
north across the desert to Egypt and the Mediterranean coast for
onward passage to Greece and Rome. Traders had also begun dealing in
spices, precious gems and textiles, which were arriving at Arabian
ports from Africa, India and beyond. According to the Roman
geographer Strabo, traffic on the Incense Road was like an army on
the march.

Grace suspects that traders setting out on the long and hazardous
journey north took Aloe vera with them. “People in the region had
probably been using and cultivating it for generations, and traders
would have carried it as a sort of living medicine chest,” she says.
It helped that the plant is easy to transport. Cut leaves stay fresh
and useful for a long time, and plantlets produced by suckering
survive a long time without soil or water – even seemingly dead ones
will grow if you plant them. “This is the most likely way it spread
to Egypt, Ancient Greece and Rome, then to India and later to the
Americas,” says Grace.

Why people chose to use and cultivate Aloe vera rather than one of
its close Arabian relatives remains a mystery. “Maybe it had larger
leaves, grew closer to town, stayed fresher during transportation or
was easier to cultivate,” says Rønsted. “But once people discovered
it had healing properties they stuck with it.” Their enthusiasm for
this plant could explain why it vanished from the wild. Aloes tend
to be restricted to specific habitats, so each species has a limited
distribution. “If it only grew in one area and everyone collected
them, it could have been wiped out that way,” suggests Rønsted. “Or
maybe its habitat now lies under a big city.” Ironically, today Aloe
vera is the only aloe that isn’t at risk of extinction, thanks to
large-scale cultivation.

And what of Cleopatra’s beauty regime? Alas, contemporary writers
failed to mention whether it included Aloe vera gel, so we may never
know for sure. But there’s little doubt she could have used it. The
plant’s reputation is surely far longer established than the queen’s
– it may even predate ancient Egypt.

Mysterious healing powers

For at least two millennia, probably far longer, countless people
around the world have put their faith in the medicinal properties of
Aloe vera.

Early accounts focus mainly on the bitter “juice”, or sap, exuded by
cells immediately beneath the leaf’s leathery epidermis. “Bitter
aloe” has been used almost continuously since classical times as a
powerful purgative, reaching the height of its popularity in the
after-dinner pills popped enthusiastically by English diners in the
18th and 19th centuries.

“There is some evidence that the active ingredients are phenolic
compounds known as anthraquinones,” says Nina Rønsted at the Natural
History Museum of Denmark in Copenhagen. Anthraquinones are what
give senna pods and rhubarb their laxative effect.

Unlike the sap, the uses of the gel found inside Aloe vera leaves
are many and varied. The modern surge of interest began in the US in
the 1930s after doctors found it helped heal skin damaged or burned
by overexposure to X-rays, and it became an increasingly popular
treatment for cancer, eczema and even hair removal at the time.

Long before this, however, the Chinese applied Aloe vera gel to
clear dermatitis. In India, people have dabbed it on sore eyes and
inflamed joints for centuries. The Javanese slathered chopped gel on
burns and drank it mixed with rosewater as a treatment for TB and
gonorrhoea. Malaysians and Mexicans pressed slabs of gel to both
aching foreheads and tumours. Jamaicans boiled the leaves with salt
to cure constipation and applied cut leaves to treat damaged nerves
and tendons. Coughs, colds, bruises, bronchitis and even baldness –
there were few complaints that someone somewhere didn’t treat with
Aloe vera.

Despite the plant’s widespread use, we lack clinical evidence that
the gel has the healing powers claimed for it, says Rønsted. She and
her colleagues are addressing this with an investigation into the
beneficial effects of polysaccharides found in various species of
aloe, comparing their ability to enhance immune defence and repair
damaged skin.

“We know too little about the chemistry of these complex sugars,”
says Rønsted. “They are very hard to analyse and we may yet find
differences in the gel of different species.” The findings might
even point to plants with greater powers than Aloe vera.
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