Vitamin A is commonly known as the anti-infection vitamin. It
plays an important role in vision and bone growth, and maintains the
surface linings of the eye and respiratory, urinary and intestinal
tracts (Pediatr Nurs, 1996; 22: 377-89, 456; Proc Nutr Soc, 1999; 58:
289-93).
Retinol, one of the most usable forms of vitamin A, is
found in animal foods, such as liver and eggs. Some plants contain
orange pigment - provitamin A carotenoid - that the liver converts to
retinol. Beta-carotene is one such carotenoid found in many foods
(Phamacol Ther, 1997; 75: 185-97; Eur J Clin Nutr, 1996; 50 [Suppl 3]:
S38-53). Beta-carotene has two roles in the body. It is converted into
vitamin A if the body needs it. If not, beta-carotene acts as an
antioxidant to protect cells from damage by harmful molecules called
free radicals.
It’s important to regularly eat foods that
provide vitamin A or beta-carotene, even though your body can store
vitamin A in the liver to help meet your needs when carotenoids or
vitamin A is low (J Nutr, 1994; 124: 1461S-6S; Eur J Clin Nutr, 1996;
50 [Suppl 3]: S7-12).
Such foods include a considerable array of
fruits and vegetables that are widely available, but which must be
eaten fresh, such as carrot, mango, sweet potato, spinach, cantaloupe,
sweet pepper, apricot, spinach, broccoli, oatmeal, tomato, peach,
papaya, orange and asparagus (Br J Nutr, 1999; 82: 203-12; Am J Clin
Nutr, 1999; 70: 1069-76; Cancer Epidemiol Biomarkers Prev, 1997; 6:
617-23; Gac Sanit, 1999; 13: 22-9; J Agric Food Chem, 1999; 47:
1576-81).
Beta-carotene is not easily assimilated by the body.
However, one study has shown that grating carrots and pureeing papaya
enhances the body’s takeup of the beta-carotene contained in these
foods (J Nutr, 2001; 131: 1497-502).
Another study suggests
that a diet rich in vitamin C and beta-carotene can increase your
lifespan. Those who eat two oranges and two carrots a day can reduce
the risk of death in middle age by over 30 per cent.
The
eating habits of 1556 male employees of a US company were tracked for
24 years. Those who ate appreciably more vitamin A, beta-carotene in
particular, reduced their risk of developing cancer or heart disease
(Am J Epidemiol, 1995; 142: 1269-78).
Indeed, provitamin A
carotenoids, such as beta-carotene, have not been proven to have any
specific adverse health effects. The conversion of carotenoids to
vitamin A is decreased when body stores are full, which puts a natural
limit on how much you can store. Although a too-high intake of
carotenoids can turn the skin yellow, this is not considered dangerous
to your health (Council for Responsible Nutrition, 1997: 26-7).
A
number of studies suggests that diets rich in beta-carotene and vitamin
A lead to a lower risk of many types of cancer (Int J Epidemiol, 1990;
19: S32-42; J Am Diet Assoc, 1996; 96: 693-702). Indeed, there is
evidence that a high intake of green and yellow vegetables, or food
sources of beta-carotene with or without vitamin A reduced the risk of
lung cancer (Int J Cancer, 1997; [Suppl 10]: 22-9).
A trial
testing the effectiveness of four nutrient combinations in preventing
throat and stomach cancers in 30,000 men and women in China found that,
after five years, there was a 13 per cent reduction in cancer deaths
among those who’d taken a combination of beta-carotene, selenium and
vitamin E (J Natl Cancer Inst, 1993; 85: 1483- 92).
However,
vitamin A can be toxic. Symptoms can arise suddenly, such as after
consuming very large amounts of vitamin A within a short time, and
include dizziness, blurred vision and muscular incoordination (J Clin
Pharmacol, 1997; 37: 551-8; Adv Exp Med Biol, 1994; 352: 187-200; Am J
Clin Nutr, 1989; 49: 358-71). Vitamin A toxicity can also cause severe
birth defects (J Am Diet Assoc, 2000; 100: 1068-70; Am J Clin Nutr,
2000; 71: 1325S-33S).
The recommended daily retinol equivalent
(RE) intake is 800 mcg for women (2664 IU) and 1000 mcg for men (3330
IU) (Int J Vit Nutr Res, 1997; 67: 71-90). A recognised safe upper
limit for vitamin A from diet and supplements is 1600-2000 mcgRE
(5328-6660 IU) a day (Am J Clin Nutr, 1989; 49: 358-71; Int J Vit Nutr
Res Suppl, 1989; 30: 42-55). Women of childbearing age should limit
their total daily intake to no more than 1600 mcgRE (5328 IU) per day,
although some nutritionists, like Dr Melvyn Werbach, suggest that as
much as 25,000 IU (7508 mcgRE) can be taken safely.
Nevertheless,
vitamin A can prove invaluable during times of infection, when our
needs begin to skyrocket, by helping the body regulate its immune
system (Int J Vit Nutr Res, 1997; 67: 71-90; Nutr Rev, 1998; 56:
S38-48). It may also help prevent bacteria and viruses from entering
your body by bolstering the skin’s defences (Proc Nutr Soc, 1998; 57:
159-65; Nutr Health, 1996; 10: 285-312; FASEB J, 1996; 10: 979-85).
As
for how much vitamin A to take during an infection, according to John
Stirling, technical director at BioCare, Birmingham, dosages vary
wildly from country to country and between practitioners. In Germany,
viral infections are treated with 10,000 IU, providing the patient
isn’t pregnant while, in the US and Australia, 25,000-50,000 IU are
given. 'Generally, English practitioners tend to be more conservative,
using 5000 IU as their baseline dosage, but going up to 10,000 IU,' he
says.
When working in a clinic in Germany, Stirling often gave
500,000 IU for seven days (for the duration of the infection or until
an adverse symptom appeared), but only with the patient under strict
medical supervision and with close laboratory monitoring. 'Certainly we
wouldn’t have done this with anyone who was pregnant, or had a history
of kidney stones, where vitamin A might increase the uptake of
calcium,' he says.
Of our six road-test products, from The Nutri
Centre as usual, three delivered vitamin A as retinol palmitate and
three used natural beta-carotene. We used Worcestershire County’s
Scientific Services laboratory for the analyses.
Says County
analyst Carol Stevens, 'The international standard units were
discontinued [in 1954 for vitamin A and 1956 for provitamin A] when
actual measurements of retinol itself could be made.' Says Stevens, 'UK
law requires all vitamin A and beta-carotene declarations to be given
as retinol equivalents or ‘mcgRE’. This is to ensure that the consumer
can make simple comparisons between products.' The Food Labelling
Regulations (1996) require that vitamin A declarations use a conversion
factor of six mcg of beta-carotene equals one mcgRE.
There’s no
doubt that the labelling on the products in our road test could have
been clearer. Indeed, not a single one stated vitamin A amounts using
the term ‘mcgRE’. Unlike multivitamins, some single-vitamin products
don’t declare all contents, as required by regulations, and many still
use international units (IU).
Although one of the preparations
cost £3.50, most of the six products we looked at cost between £7.55
and a staggering £18.95; daily-serving costs ranged from 0.02 p to
20 p per £. Why there should be such a wide disparity among these products is not clear.
Points
were awarded according to what we considered to be the best all-round
products, based on the amount of vitamin A in mcgRE and other nutrients
contained in the supplement, and overall value for money.
There
are two final caveats. Most of these supplements are potent and need to
be taken with caution. Furthermore, there are many inconsistencies
associated with vitamin A sampling techniques which can influence
laboratory results.
Vitamin A 7500iu
Manufacturer: Lamberts Healthcare
Price: £3.50 for 100 capsules
Rating: *****
At
£3.50, this was the cheapest of our six products. According to the
label, each capsule contains 2252 mcg of vitamin A from retinol
palmitate, halibut liver oil - a rich source of vitamin D - and
beta-carotene. This is the only preparation containing both retinol
palmitate and beta-carotene. Our lab found 4640 mcgRE (15,451 IU), more
than twice what was declared on the label.
This product carries a warning that pregnant women shouldn’t take vitamin A, one of only two of the six to do so.
Each capsule also contains sunflower-seed oil, a good plant source of vitamin A (Am J Clin Nutr, 2001; 74: 501-9).
This product costs a mere 0.04 p per day and offers 441,457 IU of vitamin A per £.
Dry Vitamin A 2252 ug
Manufacturer: Solgar
Price: £8.85 for 100 tablets
Rating: *****
Each
tablet has a vitamin A content of 5160 mcgRE (17,183 IU) from retinol
palmitate, the largest amount among our six products and more than
twice the stated amount. The label says this is suitable for vegans and
is 'sugar, salt and starch free'.
Vegetable cellulose and
vegetable magnesium stearate are used as binding agents. Each tablet
also contains 240 mg of di-basic calcium phosphate, a source of calcium
in nutritional supplements, but it is also an excipient - a substance
that helps to carry the tablet’s contents into the body correctly. The
label also warns that pregnant women shouldn’t be taking vitamin A.
These tablets cost only 0.09 p a day and provide 194,158 IU of vitamin A per £.
Beta Carotene 15 mg
Manufacturer: Solgar
Price: £8.75 for 60 softgels
Rating: ****
Solgar
maintains that its offerings are free of corn, yeast, wheat, soy and
dairy products, and don’t use preservatives, artificial flavours or
colours. At £8.75, this was the third most expensive product in our
test.
This contains 15 mg of 'natural form oceanic beta
carotene' - from Dunaliella salina, a single-celled saltwater algae
that is also an antioxidant and a rich source of beta-carotene, as well
as other carotenoids such as alpha-carotene, cryptoxanthin, zeaxanthin,
lutein and lycopene (J Nutr Sci Vitaminol, 1994; 40: 421-30). As per
the food-labelling regulations, Solgar has also included a listing of
these other carotenoids on the label, in descending order by weight.
The
beta-carotene content of each softgel is 23,560 mcg (3927 mcgRE or
13,077 IU), more than the stated content of 2500 mcgRE. It also
contains 49 mg of safflower oil and 500 mcg of alpha-carotene.
A daily serving costs 15 p. With this product, Solgar offers 89,671 IU of vitamin A per £.
Micellized VitaSorb-A
Manufacturer: BioCare
Price: £7.55 for 15 mL
Rating: ****
The
only liquid-based supplement of our selection, this contains 395 drops
(one drop per serving). According to the label, this little plastic
bottle contains 2500 IU of vitamin A per drop from retinol palmitate
(751 mcgRE). In fact, this delivers 2664 IU (800 mcgRE), the least in
our road test.
At £7.55, this was the fourth most costly
product in our test. A daily serving works out to be the cheapest at
0.02 p, yet the whole bottle works out to 139,375 IU per £, third in
terms of value for money.
The low dose of vitamin A per drop may be because this product is aimed at children, the only one of our sample to do so.
Natural Beta Carotene 25,000 IU Vit A Activity
Manufacturer: Nature’s Plus
Price: £18.95 for 120 softgels
Rating: ***
At
£18.95, this product is the most expensive of the six. The label claims
a beta-carotene content of 25,000 IU per serving which, according to
our calculations, works out to 7508 mcgRE in each softgel. Judging from
the County lab results, however, this refers to provitamin A. The true
vitamin A content, according to the lab report, is only 2770 mcgRE (or
9224 IU), considerably less than suggested by the label and placing it
fourth in terms of vitamin A content.
The ingredients include a
trace amount (1 IU) of vitamin E in the form of d-alpha-tocopherol (an
antioxidant which stops the vitamin A from going off) as well as soy
oil and the saltwater algae D. salina.
Unlike Solgar, Nature’s
Plus hasn’t provided a complete listing of these other ingredients, in
descending order by weight, as required by the Food Labelling
Regulations (1996).
A daily serving costs 16 p, and you only get 58,411 IU of vitamin A for your £.
One-A-Day Beta Carotene
Manufacturer: BioCare
Price: £5.90 for 30 vegetable capsules
Rating: **
Although
the label says each capsule contains 15 mg of beta-carotene, the lab
found only 10 mg, equivalent to 1667 mcgRE (5551 IU), putting this
product in last place.
There is no listing of where the
beta-carotene comes from, but we are told that each capsule contains
lecithin, vitamin E (as d-alpha-tocopherol) and cellulose.
However, in all fairness, BioCare tells us that it uses a particular type of processing that is known to skew lab analyses.
At
£5.90, this is among the cheaper purchases, but a daily serving works
out to 20 p. Also, this product gives you only 28,225 IU of vitamin A
per £, the least in our survey.
vitamin A supplements,
beta-carotene, retinol palmitate, carotenoids, Vitamin A 7500 IU, Dry
Vitamin A 2252 UG, Beta Carotene 15 mg, Micellized VitaSorb-A, Natural
Beta Carotene 25,000 Vit A Activity, One-A-Day Beta Carotene
Road
testThe best vitamin A supplement The beta-carotene controversyOver the
past decade, a number of studies have cast doubt on beta-carotene
efficacy.
Researchers from the Dartmouth Medical School, New
Hampshire, could find no strong connection between beta-carotene and a
lower risk of heart disease after studying the reports of 1118 men
(JAMA, March 6, 1996). Similarly, the National Public Health Institute
in Helsinki could find no correlation between vitamin E and
beta-carotene and a reduced risk of angina (JAMA, March 6, 1996).
More
controversially, two studies have suggested that large doses of
beta-carotene might actually cause cancer. The 1994 Alpha-Tocopherol
Beta-Carotene Cancer Prevention Study (ATBC) involved Finnish men who
were heavy smokers and alcohol drinkers. The volunteers were either
given 20 mg of synthetic beta-carotene, vitamin E, a combination of the
two, or a placebo. The rather unexpected outcome suggested that there
was an 18 per cent increase in lung cancer rates in the
beta-carotene-only group.
In another study a few years later,
based on 29,000 men, the incidence of lung cancer was greater in a
group of smokers who took a daily supplement of beta-carotene (J Natl
Cancer Inst, 1996; 88: 1560-70). The Carotene and Retinol Efficacy
Trial (CARET), a lung cancer chemoprevention trial that provided
randomised subjects with supplements of synthetic beta-carotene and
retinol (preformed vitamin A), was stopped after researchers discovered
that the subjects receiving the beta-carotene had a 46 per cent higher
risk of dying from lung cancer (Cancer Epidemiol Biomarkers Prev, 1998;
88: 1560-70).
At around the same time, however, the 12-year US
Physicians’ Health Study (PHS) - which included over 2000 smokers and,
on average, used twice as much beta-carotene for twice as long as the
ATBC and CARET studies - compared the effects of taking 50 mg of
synthetic beta-carotene every other day with a placebo in over 22,000
men and found no adverse side-effects, not even in the 11 per cent of
volunteers who were smokers (N Engl J Med, 1996; 334: 1145-9).
In
a letter sent out to customers in August 2000, Solgar’s UK technical
director, Stephen Terrass, says he’s not surprised by the PHS findings:
'Other than the contradictory findings of the other studies, the most
important fact that has not been given its due scrutiny is that the
beta-carotene used in these studies was ‘synthetic’, not ‘natural’.
Dietary intake of various other carotenoids - such as lycopene and
cryptoxanthin - is far more strongly associated with a lower cancer
risk than dietary beta-carotene intake.
'With this in mind, high
doses of synthetic beta-carotene seem to inhibit the uptake of other
dietary carotenoids. If this blocking of absorption was occurring over
the seven-year duration of these studies, this could help to explain a
statistical increase in lung cancer rates - or as the PHS trial and
others might suggest, this could help explain why the beta-carotene did
not reduce lung cancer rates. Many experts are convinced that the ATBC
results were severely impacted by the volunteers’ alcohol intake.'
According
to Terrass, alcohol causes severe oxidative damage to synthetic
beta-carotene, so removing its protective properties. 'Research has
shown that this damage could be prevented by protecting beta-carotene
with other antioxidants,' he says, underscoring the point by observing
that there was no increase in cancer rates in the ATBC volunteers who
used a combination of synthetic beta-carotene and vitamin E.
'Had
these studies employed natural beta-carotene supplements, rather than
synthetic ones, it is very likely that the results of all three studies
would have been very different - not necessarily because of the
beta-carotene itself, but rather because of the synergistic actions of
the mixture of protective carotenoids,' says Terrass. In conclusion, he
says, it seems only prudent to recommend that smokers avoid high doses
of synthetic beta-carotene, especially smokers who drink alcohol.
Lamb's liver 18,000 mcg* Green leafy vegetables, especially
Calf's liver 14,000 mcg kale (1000 mcg) and spinach (810 mcg)
Cod liver oil 18,000 mcg Broccoli 400 mcg
Butter 820 mcg Endive 333 mcg
Cheese, especially Cheddar and Carrot 2000 mcg
Parmesan 350 mcg Sweet potato (orange) 700 mcg
Single cream 220 mcg Squash 160-200 mcg
Eggs 140 mcg Sea vegetables 3900 mcg
Pumpkin 240 mcg Mango 300 mcg
Cantaloupe 300 mcg Apricot 250 mcg (dried 600 mcg)
*approximate mcg of retinol equivalent (RE) per 100 g of food
See
also the US Department of Agriculture Nutrient Data Laboratory’s
homepage at www.nal.usda.gov/fnic/foodcomp, which lists the carotenoid
content of different foods and is regularly updated.