Omega 3 Fatty Acids Have A Small But Important Antihypertensive Effect

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Omega-3 polyunsaturated fatty acids (PFAs) from foods such as fish,
nuts, seeds and vegetable oils appear to have a small antihypertensive
effect, according to the first comprehensive population based study to
look at this issue.


Dr Hirotsugu Ueshima (Shiga University,
Japan) and colleagues conducted INTERMAP, an international
cross-sectional epidemiologic study, in almost 5000 men and women in
China, Japan, the United Kingdom and the United States. They report
their findings in Hypertension.



"A large percentage of
people between ages 20 and 60 have a rise in blood pressure, and by
middle age many have high blood pressure. We're looking at dietary
factors that may help prevent that rise, and omega-3 fatty acids are a
small, but important piece of the action," says co-author Dr Jeremiah
Stamler (Feinberg School of Medicine at Northwestern University,
Chicago) in an American Hypertension Association media release.


Japanese Have Highest Consumption of Omega-3 PFAs


The
researchers explain that short-term studies had already indicated that
taking dietary supplements of omega-3 PFAs could lower blood pressure
in people with hypertension, but the impact of omega-3 PFAs in food and
in people without hypertension was previously unknown.



INTERMAP
is a large study of lifestyle factors, particularly diet habits and
nutrients, and their influence on blood pressure in 4,680 men and
women, ages 40 - 59, living in 17 different areas of Japan, China, the
United Kingdom and the United States, constituting an ethnically
diverse population from a variety of socioeconomic backgrounds. All
participants completed four in-depth 24-hour dietary recalls and two
timed 24-hour urine collections, supplied information on their use of
alcohol, dietary supplements and medications, and had their blood
pressure measured twice at each of four study visits.



The amount
of omega-3 PFAs in the diet for all 4,680 participants was calculated,
and found to average around 2.0 grams per day. The researchers then
compared blood pressure in people consuming higher versus lower amounts
of omega-3 PFAs (about 0.7 percentage points higher as a percentage of
their daily calorie intake; about 1.9 grams per day higher).



Of
the four countries studied, the people in Japan had the greatest intake
of omega-3 PFAs, both from vegetable sources and fish.



In
general, the effect size of consuming more omega-3 PFAs was small.
After multi-variate adjustment for factors such as age, gender, height,
weight, exercise, alcohol consumption, salt intake and other dietary
factors, diets rich in omega-3 PFAs were associated with < 1 mm Hg
lower systolic and diastolic blood pressures.



The effect size was
larger for non-hypertensive people, and for those not reporting
lifestyle modification (eg special diet, use of nutritional
supplements), cardiovascular disease or diabetes, or prescribed
medication for major chronic diseases.



But despite the effect
being small, it is nevertheless important, say the authors, citing
studies that show that a decrease of 2 mm Hg of blood pressure reduces
the population-wide average death rate from stroke by an estimated 6%
and from coronary heart disease by 4%.



"With blood pressure,
every millimeter counts. The effect of each nutrient is apparently
small but independent, so together they can add up to a substantial
impact on blood pressure," says Ueshima. "If you can reduce blood
pressure a few millimeters from eating less salt, losing a few pounds,
avoiding heavy drinking, eating more vegetables, whole grains and
fruits and getting more omega-3 fatty acids, then you've made a big
difference."


Vegetables and Nuts Just as Important as Fish


Ueshima
et al say their data from INTERMAP on food omega-3 PFAs and blood
pressure "are concordant with results from meta-analyses of randomized
trials assessing whether omega-3 PFA supplements (mostly fish oils)
influence BP." In particular, "our data are similar qualitatively and
quantitatively in indicating a low-order favorable BP effect, including
in non-hypertensive persons," they note.



They also found that
omega-3 PFAs from nuts, seeds and vegetable oils — such as walnuts and
flaxseed — had just as much impact on blood pressure as omega-3 PFAs
from fish sources.



The authors say people should increase their
intake of unsalted, cooked fish such as trout, mackerel, herring and
sardines, and consume vegetable products high in linolenic acid (an
omega-3 PFA), such as unsalted walnuts, flax seed, canola oil and soy
bean oil.



"We want to emphasize that you can get plenty of the
omega-3 fatty acids by eating modest portions with a reasonable amount
of calories and fat," Stamler says.



And the benefits of omega-3
fatty acids may extend beyond blood pressure lowering, they add, noting
that they have also been shown to favorably influence dyslipidemia, and
have anticoagulant and antiarrhythmic effects.



Hypertension. Published online June 4, 2007.



The complete contents of Heartwire, a professional news service of WebMD, can be found at www.theheart.org, a Web site for cardiovascular healthcare professionals.


Clinical Context


According to the authors of the current
study, small reductions in BP have been associated with clinically
important risk reductions for stroke and cardiovascular disease and a
2-mm Hg reduction in systolic blood pressure (SBP) may be associated
with reduction in mortality of 6% from stroke and 4% from
cardiovascular disease. There is some evidence of enhanced effects of
omega-3 PFA intake on cardiovascular disease risk via potential
mechanisms of blood pressure (BP) reduction, favorable effects on
dyslipidemia, and anticoagulant and antiarrhythmic effects. Other
nutrients such as minerals, vegetable proteins, sugars, and sodium
chloride may also be associated with reduced cardiovascular disease
risk.



The INTERMAP study is an observational study that involved 17
population-based cohorts from China, Japan, the United Kingdom, and the
United States in whom BP was measured and dietary intake assessed to
examine the effect size of dietary omega-3 PFA intake on SBP and
diastolic blood pressure (DBP) in individuals with and without
hypertension.


Study Highlights
  • Included were 4680 men and women aged 40 to 59 years from 4
    countries who provided plausible dietary information and attended 4
    study visits.
  • Visits 1 and 2 took place on consecutive days, and visits 3 and 4 took place within 3 weeks and occurred on 2 consecutive days.
  • BP was measured after the bladder was emptied and 5 minutes' rest, using standard protocol.
  • Dietary data were collected by a trained interviewer using the in-depth multipass 24-hour recall method.
  • All foods and drinks consumed within 24 hours, including supplements and alcohol, were recorded.
  • Body mass index and urinary metabolites were measured.
  • The average SBP ranged from 117.2 (Japan) to 121.3 mm Hg (China).
  • The average DBP ranged from 73.2 (China) to 77.3 mm Hg (United Kingdom).
  • Mean body mass index and energy intake were lower for Japanese and Chinese participants and highest for US patients.
  • Mean total omega-3 PFA intake from foods was highest in Japan
    (1.35% of total calories) and lowest in China (0.55% of total calories).
  • Linoleic acid accounted for 78% of all omega-3 PFA intake (60% in Japan and 98% in China).
  • Main food groups supplying long-chain omega-3 PFAs were, for all
    4680 participants, fish and fish products, shellfish and shellfish
    products, red meats, poultry, and eggs and their products.
  • For all 4680 participants, a 2-SD higher intake of omega-3 PFAs was
    associated with lower SBP (magnitude, -0.4 to -0.6 mm Hg) and lower DBP
    (magnitude, -0.5 to -0.6 mm Hg).
  • For individuals with untreated high BP (11.8% of men and 5.7% of
    women), a 2-SD higher intake of omega-3 PFAs was associated with SBP
    change of -1.01 mm Hg and a DBP change of -0.98 mm Hg.
  • In individuals without hypertension (n = 3671), SBP and DBP
    differences were greater than for the entire cohort at -0.74 and -0.72
    mm Hg, respectively.
  • After adjustment for 17 variables, the SBP/DBP differences were
    -0.55/-0.57 mm Hg for all participants, -1.01/-0.98 mm Hg for 2238
    persons without medical or dietary interventions, and -0.91/-0.92 mm Hg
    for persons without hypertension.
  • SBP differences were nonsignificantly larger for UK and US
    participants, and DBP differences were larger for Chinese and US
    participants.
  • Linoleic acid intake was also inversely related to SBP at a
    magnitude of -0.60 to -0.97 mm Hg for an intake that was 2 SDs higher.


Pearls for Practice
  • Intake of omega-3 PFAs of 2 SDs above the mean is associated with
    small reductions in SBP and DBP in populations both with and without
    hypertension.
  • Intake of omega-3 PFAs of 2 SDs above the mean has a larger effect
    on persons without medical or dietary interventions and persons without
    hypertension vs the general population



Submitted by DMorgan on Mon, 06/25/2007 - 8:48pm.