A diet high in vegetables rich in beta-carotene
appears to reduce the risk of developing certain cancers.
However, in a large study of 29,000 men, when a beta-
carotene dietary supplement was taken by men who
smoked, they developed lung cancer at a rate 18%
higher and died at a rate 8% higher than men who did
not take the supplement. Another study that gave men
dietary supplements of beta-carotene and vitamin A
was stopped when researchers found the men receiving
the beta-carotene had a 46% greater chance of dying
from lung cancer than those who did not take it. The
official position of the IOM is that ‘‘beta-carotene sup-
plements are not advisable for the general population.’’
ALPHA-CAROTENE.Alpha-carotene is the lesser-
known cousin of beta-carotene. It also is a provitamin
A carotenoid, but it takes 24 mcg of alpha-carotene to
make 1 mcg of retinol. Good sources of alpha-carotene
include pumpkin, carrots, winter squash, collard greens,
raw tomatoes, tangerines, and peas. Less research has
been done on alpha-carotene than beta-carotene, but it is
not recommended as a dietary supplement.
BETA-CRYPTOXANTHIN.Beta-cryptoxanthin is also
a provitamin A carotenoid. It takes 24 mcg of beta-
cryptoxanthin to make 1 mcg of retinol. Good sources
of beta-cryptoxanthin include pumpkin, red bell pep-
pers, papaya, tangerines, nectarines, oranges and
orange juice, carrots, yellow corn, and watermelon.
LUTEIN AND ZEAXANTHIN.Lutein and zeaxanthin
do not have vitamin A activity. They are the only
carotenoids found in the human eye. It has been pro-
posed, but not proven, that they may help slow the
development of cataracts. Cataracts are changes in the
lens of the eye that result in clouding and vision loss.
These carotenoids are also found in the retina. They
absorb light in the blue wavelength range. It is theorized
that they can help slow or prevent age-related break-
down of the retina (age-related macular degeneration),
a common cause of vision loss in the elderly. Good
sources of lutein and zeaxanthin include spinach, kale,
turnip, collard, and mustard greens, summer squash,
peas, broccoli, Brussels sprouts, and yellow corn.
LYCOPENE.Lycopene is the carotenoid that gives
tomatoes, watermelons, and guavas their reddish
color. In the American diet, almost all dietary lyco-
pene comes from tomato products.
The relationship between dietary intake of lyco-
pene and the risk of men developingprostatecancer is
of great interest to researchers. One large study of
58,000 Dutch men found no relationship between the
two. However, an analysis of 21 studies examining the
relationship between lycopene intake and prostate
cancer found that men with the highest dietary intakeof lycopene were less likely to develop prostate cancer.
The reduction appeared real, but modest—11–19%.Precautions
The relationship between lung cancer and beta-
carotene strongly suggests that all carotenoids should
be obtained through diet and not through dietary
supplements. There is also no information on the
safety of carotenoid dietary supplements in children
or women who are either pregnant orbreastfeeding.Interactions
Interactions of specific carotenoids with drugs,
herbs, and dietary supplements have not been well
studied. In general, cholesterol-lowering drugs,orli-
stat (Xenical or Alli), and mineral oil reduce the
absorption of carotenoids from the intestine, but it is
not known whether this has an effect on health.Complications
There are no identified complications from caro-
tenoid deficiency.
Beta-carotene supplements of 30 mg per day or
more or excessive consumption of carrots and other
beta-carotene rich food can cause the skin to become
yellow, a condition called carotenodermia. Caroteno-
dermia is not associated with any health problems and
disappears when beta-carotene intake is reduced.KEY TERMS
Antioxidant—A molecule that prevents oxidation.
In the body antioxidants attach to other molecules
called free radicals and prevent the free radicals
from causing damage to cell walls, DNA, and
other parts of the cell.
Cell differentiation—The process by which stem
cells develop into different types of specialized
cells such as skin, heart, muscle, and blood cells.
Dietary supplement—A product, such as a vitamin,
mineral, herb, amino acid, or enzyme, intended to
be consumed in addition to an individual’s diet
with the expectation that it will improve health.
Provitamin—A substance the body can convert
into a vitamin.
Retina—The layer of light-sensitive cells on the
back of the eyeball that function in converting
light into nerve impulses.Carotenoids