Waarom
groenten tegen hoge bloeddruk?*
Een
Zweeds onderzoek geeft antwoord op de vraag waarom groeten helpen tegen hoge
bloeddruk. Nitraten uit groenten zoals o.a. spinazie en sla bevorderen de
productie van stikstofoxide (NO), die de bloedvaten soepel maakt. Toch is dit
maar een gedeeltelijke verklaring voor het gezondheidseffect van het dieet. Om
een merkbaar effect te ondervinden zou een mens bijvoorbeeld al 250 gram
spinazie moeten eten. Er moeten nog meer gunstige effecten zijn die nog nader
worden onderzocht. Hoge bloeddruk vormt een gevaar voor het hart, de hersenen,
nieren, ogen en bloedvaten en nitraten in groenten kunnen voor een deel
uitleggen waarom de Amerikaanse regering gekozen heeft voor het D(ietary)A(pproaches
to)S(stop)H(ypertension) programma tegen hoge bloeddruk. DASH adviseert veel
groenten en fruit.
Nitrates
May Explain Success of Blood-Pressure Diet
A small Swedish study could help explain
why the U.S. government-recommended DASH diet helps fight high blood pressure.
DASH -- Dietary Approaches to Stop
Hypertension -- recommends eating lots of vegetables and fruits. The Swedish
study indicates that the nitrates in foods such as spinach, beet root and
lettuce spur production in the body of nitric oxide, a molecule that relaxes
blood vessels.
"What this study suggests is that the
well-known beneficial effects of vegetables on cardiovascular disease may at
least partly depend on nitrate," said Dr. Eddie Weitzberg, professor of
anesthesiology and intensive care at the Karolinska Institute in Stockholm, and
a leader of the study.
Weitzberg and his colleagues had 17 young
adults alternately take dietary supplements of sodium nitrate or a placebo, an
inactive substance. There was no reduction in systolic blood pressure (the
higher number of a 120/80 reading) when they took the nitrate, but a 3.7-point
reduction in diastolic pressure (the lower number) when they did.
"This reduction is in the same
magnitude as in the cited DASH study, where those subjects were put on a fruit
and vegetable diet for 11 weeks," Weitzberg noted.
The findings are published in the the New
England Journal of Medicine.
The study suggests a new pathway for nitric
oxide production in the body, Weitzberg said. "Ingested nitrate is reduced
by oral, commensal, bacteria to nitrite, which can further be reduced to nitric
oxide," he explained.
It's too early to recommend nitrate
supplements, Weitzberg said. "One should be extremely cautious to draw
strong conclusions from our small trial, since we have not yet investigated if
the observed effects are withstanding after a longer period of dietary nitrate,"
he said.
And nitrate is considered "a substance
that should be avoided or at least reduced in our drinking water and food,"
Weitzberg noted, because it is believed to increase the risk of a rare blood
condition, methemoglobulinemia, and perhaps of cancer.
"Everyone has been asking why this
[the DASH] diet worked," said Dr. Steven Nissen, chairman of cardiovascular
medicine at the Cleveland Clinic, adding that the study does provide evidence
for the possible effect of the sodium nitrate in green, leafy vegetables.
But Nissen was quick with a caveat -- there
isn't all that much nitrate in those vegetables. "Too get as much nitrate
as was given in the study, you would have to eat about half a pound of spinach,"
he said. "As a practical issue, it's hard to ingest 250 grams of
nitrate-rich foods."
Weitzberg said research on nitrates and
high blood pressure will continue at the Karolinska Institute, in part because
the researchers aren't sure about the mechanism of the nitrate effect.
"It is not very easy to unravel the
exact underlying mechanisms," he said. "We are naturally planning to
look into this more deeply."
(Jan. 2007) (Opm. Alle groenten bevatten meer of minder nitraten. Teveel kan ook weer niet goed zijn, kijk maar bij nitraten. Het hele DASH programma vindt u al geruime tijd bij Specifiek advies, u vindt het ook hier.)