No other herb has served as many culinary and medicinal roles in
as many cultures as garlic (Allium sativum L). Indeed, over the past 20
years, there have been more than 2000 papers published on garlic
chemistry, pharmacology and clinical applications (Koch HP and Lawson
LD, Garlic: The Science and Therapeutic Application of Allium sativum
L. and Related Species, Baltimore: Williams & Wilkins, 1996).
is rich in antioxidant phytochemicals such as organosulphur compounds
and flavonoids, both capable of scavenging tissue-damaging free
radicals (Cancer J, 1990; 3: 20-1). Although the mechanisms of all
garlic components are not known, many of its heart-protective,
anticancer, anti-inflammatory and antiageing effects are thought to be
due to these antioxidant actions (Planta Med, 1994; 60: 417-20; Planta
Med, 1992; 58: 468-9; J Pharm Pharmacol, 1993; 49: 908-11; Neurochem
Int, 1996; 29: 135-43).
Science has focused particularly on the
potential of garlic in treating atherosclerosis. Studies show that
garlic thins the blood and lowers ‘bad’ LDL cholesterol and
triglycerides (Atherosclerosis, 1999; 144: 237-49). Trials using
different forms of garlic providing a daily dose of around 10 mg of
alliin, or a total allicin potential of 4000 mcg, have found that total
cholesterol was reduc-ed by 10-12 per cent, and LDL and triglycer-ides
by around 15 per cent each. In addition, some studies found that ‘good’
HDL cholesterol increased by 10 per cent (Ann Intern Med, 1993; 119:
599-605; Am J Med, 1993; 94: 632-5; Arzneim Forsch, 1990; 40: 1111-6;
Arzneim Forsch, 1992; 42: 1223-7; Br J Clin Pharmacol, 1989; 128:
But not all garlic studies are positive (J R Coll
Phys [Lond], 1996; 30: 329-34; Athero-sclerosis, 1995; 113: 219-25;
Arch Intern Med, 1998; 158: 1189-94). One controversial study using
steam-distilled garlic found no benefit at all (JAMA, 1998; 279:
1900-2). However, this trial confirms the importance of using the right
preparation - steam-distilled garlic has virtually no beneficial
sulphides and no allicin.
A report by the US Agency for
Healthcare Research and Quality (AHRQ; see
www.ahrq.gov/clinic/garlicsum for links to the full report) reviewed
all randomised, controlled trials of more than four weeks, and
concluded that garlic has a modest but statistically significant effect
in lowering LDL and triglyceride, but no overall effect on total or HDL
Cancer prevention is
another touted benefit of garlic, but the findings are mixed. However,
it’s probably fair to say that if garlic has any effect at all, it is
not as a cure, but as a possible preventative for certain types of
cancer. The organosulphur components of aged garlic can block
carcinogens and prevent oesophagus, colon, lung, breast, prostate and
stomach cancers - at least in the lab (Carcinogenesis, 1993; 14:
1627-31; Nutr Cancer, 1997; 27: 186-91; Nutr Rev, 1996; 54: S82-6).
specific trials are lacking, the AHRQ noted that population studies
show that people who regularly eat lots of garlic have a lower risk of
developing certain cancers - laryngeal, gastric, colorectal and
endometrial - than those who eat little or no garlic. This has been
borne out by observational studies and meta-analyses (J Nutr, 2001;
131: 1032S-40S; Am J Clin Nutr, 2000; 72: 1047-52).
Chinese study of a population with a high incidence of stomach cancer,
those in the highest quarter of garlic consumption had 40 per cent less
cancer risk than those in the lowest quarter (J Natl Cancer Inst, 1989;
A study in Iowa looked at the diets of over 40,000
women and found that those who consumed the most garlic had the lowest
risk of colon cancer (Am J Epidemiol, 1994; 139: 1-15). However, a
Dutch study of more than 120,000 men and women found no relationship
between garlic supplementation and breast, colon, rectal or lung cancer
prevention (Carcinogenesis, 1996; 17: 477-84), which seems to reinforce
the view that it is fresh garlic that provides the most effective
Most of us have been taught to buy
standardised garlic supplements with a guaranteed allicin yield, or
allicin potential. But this doesn’t necessarily mean that we’re getting
what we think we are.
The allicin yield quoted on many labels
generally refers to the potential of the alliin in the product to be
converted into allicin by the enzyme alliinase. This yield can only be
guaranteed at the point of manufacture as allicin degrades quickly. By
the time it reaches the consumer, it may be a very different product.
too high a heat during processing and prolonged storage at high
temperatures can destroy alliin, resulting in low allicin potential.
Not surprisingly, research shows that most commercial products don’t
contain allicin (Planta Med, 1991; 57: 363-70).
reason why older garlic studies were mostly positive while newer ones
have shown less benefit was hinted at by a reanalysis of the garlic
products used in all studies carried out between 1989 and 1997.
According to the US researchers, the older lots were more resistant to
stomach acid and therefore released three times as much allicin than
the newer ones (Planta Med, 2001; 67: 13-8). So, could it be that in
the race to produce newer and better products, pharmaceutical science
has managed to take a giant step backward?
At any rate, the
focus on allicin content of garlic supplements may be inappropriate
since allicin is just one of the dozens of the herb’s active
components. Ajoene (formed by combining allicin and diallyl disulphide)
has proven antiplatelet and antibiotic activity. A number of
constituents - including 33 identified sulphur compounds, 17 amino
acids, germanium, calcium, copper, iron, potassium, magnesium,
selenium, zinc, and vitamins A, B1 and C - have known healthful actions
in the body (Br J Clin Pharmacol, 1989; 28: 535-44; Phytother Res,
1988; 2: 196-7).
Allicin may be only indirectly involved in
garlic’s blood-thinning ability (Thromb Res, 1992; 65: 141-56). As
allicin doesn’t readily enter the blood circulation, it may be that,
once ingested, its role consists of its being converted into other
bioavailable compounds that produce the anticlotting effects (Thromb
Res, 1992; 65: 141-56).
In addition, many of garlic’s
sulphur-containing compounds - vinyldithiins, ajoene and S-allyl
cysteine - and other constituents are quickly absorbed from the
digestive tract, then extensively and rapidly metabolised. With regular
ingestion, these can be detected in the blood and tissues. Allicin, on
the other hand, cannot be detected in the blood or urine after
ingestion of either raw garlic or pure allicin (Planta Med, 1992; 58:
345-50). For this reason, many scientists argue that it cannot be the
primary active ingredient in garlic.
Experts now believe there
is no single constituent of garlic that is its main active ingredient.
Rather, the range of constituents in garlic act in synergy to produce a
variety of healthful benefits. It may therefore make more sense to seek
out minimally processed supplements that include as many of the
health-giving constituents of garlic as possible (see box above).
Some final thoughts
effectiveness of garlic preparations can be altered in other ways. Like
all herbs, the taste and smell of garlic is a kind of in-your-mouth
quality control. Without them, it’s likely to be an inferior product.
Odourless garlic preparations are usually cooked; this inactivates
alliinase, the enzyme that breaks down alliin to help make allicin. Or
an odour-masking compound such as chlorophyll is added to the
preparation, although such additions are rarely effective.
drastic is odour-controlled garlic, which is usually coated with a
glaze or uses a sturdy capsule to make sure the garlic is released only
in the gut, where it is unlikely to produce ‘garlic breath’ or reflux.
the plus side, 200 mg daily - around 70 cloves - has no known
side-effects. To be toxic to the stomach and liver, you’d have to eat
300-500 mashed cloves in one sitting. Many people ‘overdose’ on fresh
garlic in the belief that it’s good for them, but the most likely
effect of eating four or more cloves in one go is nausea and vomiting.
of its anticlotting properties, garlic supplements should not be taken
with drugs such as heparin, warfarin and coumarin derivatives, and not
before surgery, as this could lead to uncontrollable bleeding. These
small considerations aside, garlic used properly and for the right
indications is still one of our most valuable herbs.
our nine randomly selected products, only about half provided good
label information. Also, allicin content was listed in different ways
so that those who don’t know that ‘mcg’ and ‘ug’ mean the same thing
might rightly feel confused.
Price: £5.79 (30 capsules)
has used a maceration process for a product that is 'rich in allicin'
and also contains the active byproducts of allicin conversion, such as
ajoenes, vinyldithiins and polysulphides. Indeed, recent research
suggests that maceration is the only process that leaves significant
quantities of ajoenes and vinyldithiins.
The softgel capsule
releases the macerate only in the gut, ensuring effective odour
control. The label offers a good amount of useful information. However,
at one capsule a day, this will cost you 19 p, although the product’s
apparent quality may tip the balance for most consumers.
Maximum Garlic 6500
Distributor: Holland & Barrett
Price: £6.99 (60 tablets)
of these high-potency tablets contains 650 mg of standardised garlic
powder with a guaranteed allicin yield of 6500 mcg. The label also
lists the total thiosulphinate yield (6500 mcg/ug), alliin yield
(14,500 mcg/ug) and gamma-glutamylcysteine (5200 mcg/ug), which seems
But the product also contains binders, fillers and
colouring (titanium dioxide), and uses a shellac glaze (an insect
byproduct, and so unsuitable for vegans or strict vegetarians). It is
odour-controlled by the inclusion of anise oil, which may be just as
hard on sensitive stomachs as garlic oil.
Although the highest-potency product we looked at, it lies in the middle of the price range, with each capsule costing 12 p.
One-a-Day Garlic Plus
Price: £6.25 (30 capsules)
offering contains 400 mg of garlic concentrate (plus 200 mg of biotin)
in a vegetarian capsule. Other than that, the label provides no
information on how the product was produced or what the potential
allicin yield is. It would be reasonable for a consumer to be
suspicious of any product with such vague labelling. For the record,
these capsules contain a powdered concentrate.
At one capsule daily, they were the most expensive at 21 p per day.
Whole Garlic Bulb
Price: £4.49 (60 capsules)
of these capsules contains 300 mg of freeze-dried garlic (equal to 1070
mg fresh). FSC claims that freeze-drying the whole clove ensures that
all the active ingredients of the fresh herb are maintained. In
reality, it’s not much different from any other drying process, though
these products may contain slightly more S-allyl cysteine.
product is made from 100 per cent Chinese garlic - although the
relevance of this is not clear - and doesn’t use a deodorising process
because, says the manufacturer, it reduces the potency of the active
constituents (a claim borne out by research). Odour may not be a
problem, however, since these capsules are likely to dissolve in the
gut. The label contains plenty of information, some of it useful.
The recommended one or two tablets daily would cost you just 7 p each.
Distributor: Lichtwer Pharma
Price: £3.99 (30 tablets)
manufacturer tells us that Kwai contains all the constituents of fresh,
organically grown Chinese garlic. Each tablet is coated 60 times for
odour control. The active ingredients are 300 mg of dried standardised
garlic extract, and each tablet has a guaranteed allicin yield of 1800
Kwai has been used in many studies of the effectiveness
of garlic, but not always with the consistently good results, as
Lichtwer would have us believe. This product uses a huge number of
excipients, including sugar, lactose, glucose syrup, titanium dioxide
and polysorbate 20, and strict vegetarians and vegans should note that
this product also uses a shellac glaze.
Taking the suggested one tablet a day would set you back 13 p - fairly pricey for what you’re actually getting.
Price: £4.95 (60 tablets)
box boasts that Wassen garlic can help maintain a healthy heart. Tipped
as highly odour-controlled and high in potency, these tablets contain
the equivalent of 960 mg of fresh garlic (or 1600 mcg of allicin). They
are heavily coated with a glaze similar to Kwai’s and contain just as
many excipients, including sucrose, iron oxides, acacia powder and
titanium dioxide. Consumers may be justifiably suspicious of so many
extras. One tablet a day would cost you 8 p a day.
Distributor: Natural Brand
Price: £4.29 (90 capsules)
gelatine capsule contains 3 mg of garlic oil - equivalent, says the
manufacturer, to 15 mg of fresh garlic. Otherwise, the label provides
little else upon which to make a decision. The product has the strong
garlicky smell characteristic of garlic oil, which some may find
The recommended intake is one capsule daily,
costing 5 p - reasonable until you consider that, as a garlic oil
supplement, it’s likely to contain only minute quantities of
oil-soluble diallyl sulphide and diallyl disulphide, and no allicin.
Concentrated Garlic One a Day
Price: £4.90 (30 tablets)
special offer of three-for-the-price-of-two makes this seem like good
value - until you read the label. These low-dose tablets contain 300 mg
of garlic powder and have a guaranteed allicin yield of 1800 mcg.
label also boasts that these tablets can help maintain healthy
cholesterol levels and a healthy heart - although, at one a day, this
dose is far below the 4000 mcg found to be effective in scientific
studies. This also has loads of excipients, including the synthetic
binder polyvinyl pyrrolidone.
Even at the special price offer, these tablets cost 11 p a day, more than some of the better mid-range products we reviewed.
Price: £2.59 (30 capsules)
beneficial effects of garlic consumption - a healthy heart, good
circulation and a healthy digestive system - are listed on the box, but
each capsule contains only 2 mg of odourless garlic, equivalent to 200
mg of fresh garlic. It uses no preservatives, artificial colours or
flavours, though the gelatine capsule is unsuitable for vegetarians.
surprisingly, there’s no mention of allicin yield - probably because
odourless garlic is devoid of the allinase necessary to make allicin.
In addition, this product uses odourless garlic powder in sunflowerseed
oil. For 9 p a capsule, this gives you a low dose of something not very
garlic supplements, allicin, alliinase, antioxidants,
atherosclerosis, lipid-lowering, cancer prevention, blood thinning,
side effects, benefits
Road testChoosing garlic
wiselyDifferent ways of producing garlic supplements produce markedly
different products (J Nutr, 2001; 131: 955S-62S; Minnesota Pharm, 1999;
53: 13-8, 24-6; WHO Monographs on Selected Medicinal Plants, vol 1,
Geneva: World Health Organization, 1999).
Active ingredients Useful for
Fresh None; allowing Alliin, allyl
sulphides May prevent cancer
10 minutes including S-allyl (e.g.
between peeling cysteine, plus a range may also
and cutting/cooking of useful minerals cholesterol, boost
preserves beneficial and other nutrients immunity and aid
constituents cardiovascular health
Dehydrated Cloves are sliced
or Similar to fresh, but Stimulates immunity,
powder crushed, dried
and slightly more alliin and free-radical scavenger,
when S-allyl cysteine; some improves cholesterol,
low oil-soluble sulphur aids cardiovascular
temperatures, may compounds; enteric health
have slightly more coating protects alliinase
active constituents from stomach acid
Whole or sliced Mostly water-soluble May lower cholesterol,
cloves soaked in sulphur compounds may prevent cancer;
extracting solution (S-allyl cysteine, S-allyl gentler on stomach,
or (e.g. water, alcohol) mercaptocysteine); less odour; water-
garlic) for variable time small amounts of soluble compounds
to 20 months oil-soluble compounds; less cytotoxic than
no alliicin or allyl oil-soluble compounds
Whole cloves ground During processing, Acts as a free-radical
into vegetable oil at some alliin converted scavenger, improves
low temperatures to allicin,which converts cholesterol levels,
other beneficial aids heart health,
compounds (dithiins, boosts
Whole cloves ground Minute quantities May be useful
in water, heat (steam)- of oil-soluble sulphides topically, but few
distilled or extracted (e.g. diallyl sulphide, benefits when
alcohol; usually diallyl disulphide), ingested; toxic in
1% garlic oil but no allicin very large amounts
in vegetable-oil base