General Description
Evening primrose (Oenothera biennis, also known as willow herb,
fever plant, or tree primrose) is native to North America east of
the Rockies to the Atlantic coast. A biennial plant that grows wild
in dry meadows and along roadsides, evening primrose has an erect,
hairy stem that bears alternate, hairy leaves, which grow from 3
to 6 inches long and taper to a point. The plant flowers from June
to October, bearing yellow, lemon-scented blossoms, 1 to 2 1/2 inches
across, which open at dusk. The fruit of the plant is an oblong,
hairy capsule, which contains small, reddish-brown seeds. Although
the Native Americans and early European settlers used the whole
plant for a variety of health applications, modern use has centered
on the oil pressed from the seeds (EPO). This oil is primarily composed
of linoleic acid, and omega-6 essential fatty acid found in most
vegetable oils, but it also contains a significant amount of gamma
linolenic acid (GLA), an omega-6 oil found in only a few plant seeds.
Borage oil and black currant seed oil are also rich sources of GLA.
Health applications
Primary functions
Although EPO is about 72% linoleic acid, its 9% GLA portion is considered
the primary active ingredient. The body converts GLA into prostaglandin
E1 (PGE1), a hormone-like substance that helps regulate allergic
reactions, inflammation, blood pressure, heart function, and the
production of hormones. Linoleic acid can be converted into GLA
(and subsequently PGE1) in the body, but many dietary factors and
health conditions can interfere with this process. For this reason,
GLA is considered the more reliable PGE1 precursor.
Diabetes
Diabetes has been associated with impaired conversion of linoleic
acid into GLA,1,2 which may interfere with
prostaglandin production and lead to defective nerve function.3
Studies have shown that supplementation with EPO may reverse the
altered fatty acid and prostaglandin metabolism in diabetic patients
4 and may play a useful role in the prevention and
treatment of diabetic nerve disfunction.5,6
Some studies indicate that EPO may be helpful in other disorders
associated with prostaglandin imbalances, such as rheumatoid arthritis7,8
and Raynaud's phenomenon.9
Premenstrual syndrome
EPO supplements are commonly used by women seeking natural ways
to alleviate the symptoms of PMS. A number of studies indicate
EPO can improve many PMS symptoms such as depression, irritability,
fluid retention, and breast pain.10-13 Although
EPO's method of action in PMS is unclear, some scientists attribute
its effects to increased PGE1 production, which may attenuate
the action of some hormones such as prolactin.11
Skin disorders
Omega-6 fatty acid deficiencies have been associated with inflammatory
skin conditions in both animals and humans. Studies on subjects
with eczema showed elevated levels of linoleic acid and reduced
levels of GLA, suggesting impaired conversion of linoleic acid
to GLA.14 A number of studies indicate EPO
supplements can improve symptoms in many eczema sufferers.14-18
Dosage/toxicity
Studies on EPO have used doses ranging from 2 to 4 grams per day,
and it appears to be well tolerated at this dosage range. For
PMS, the most commonly recommended dosage is 2 grams per day for
2 weeks preceding menstruation. Because other nutrients including
magnesium, zinc, niacin, vitamin B-6, and vitamin C are needed
along with EPO for the body to produce PGE1,11
some experts recommend taking EPO with a multivitamin that supplies
these nutrients. EPO has no known toxicity. |
