[PHNUTR-L] Daidzein from soy linked to heart health benefits

[Kathrynne Holden, MS, RD]

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Daidzein from soy linked to heart health benefits

By Stephen Daniells

23/06/2006 - Increasing levels of daidzein, an isoflavone found in soy, 
have been linked to significant improvements in cholesterol levels and 
could boost heart health, says a new study.

“These results are the first to demonstrate a beneficial association 
between blood levels of the phytoestrogen daidzein and lipoproteins in 
human subjects,” wrote lead author Noel Bairey Merz from the University 
of Pittsburgh Graduate School of Public Health.

A recent scientific statement by the American Heart Association (AHA) in 
the journal Circulation concluded that soy had little effect on 
cholesterol levels, and raised doubts about health claims associated 
with soy.

Dr Frank Sacks, a member of the AHA panel, said in January: “It's really 
clear that isoflavones don't contribute anything to cardiovascular 
benefits.”

But the new study, published in The Journal of Clinical Endocrinology 
and Metabolism (Vol. 91, pp. 2209-2213), reports that high blood levels 
of daidzein were associated with favourable lipoprotein profiles.

If its findings are reproduced in future studies, they might lead to a 
re-evaluation of the science that led AHA to its conclusion.

Half of the women recruited for the Women's Ischemia Syndrome Evaluation 
(WISE) study (483 subjects; BMI 29.4; average age 58; 79 per cent 
post-menopausal) were chosen for this research. All the volunteers had 
at least one coronary risk factor. Blood samples were taken and levels 
of the soy isoflavones daidzein and genistein were measured.

Blood levels of total cholesterol (TC), triglyceride (TG) and 
HDL-cholesterol (HDL-C) were determined by an enzymatic assay. 
LDL-cholesterol (LDL-C) levels were calculated using the Friedewald formula.

The researchers found that increasing levels of daidzein were associated 
with decreasing levels of TG and increasing HDL-C levels. Women with the 
highest blood daidzein levels (more than 13.2 nanograms per millilitre) 
had 17 per cent lower TG levels and 5 per cent higher HDL-C levels than 
women with the lowest levels (less than 3.2 nanograms per millilitre).

When the researchers examined the data taking into account levels of the 
female hormone estradiol, they found that the link between daidzein 
blood levels and lipid profiles was stronger in women with low estradiol 
levels. The relationship between daidzein and blood lipids was not 
significant for women with high estradiol levels.

“Our findings of the beneficial association between daidzein and 
lipoproteins being dominantly evident among women with low blood 
oestrogen levels supports the idea that daidzein may operate, in part at 
least, via an oestrogen receptor mechanism,” said the researchers.

No relationship between blood levels of the isoflavone genistein and 
blood lipoprotein levels was found.

“These and prior studies suggest that cardiovascular risk reduction 
strategies in women should consider dietary intake of food products, 
such as soy, which elevate blood daidzein levels, consistent with recent 
recommendations,” concluded Bairey Merz.

This study has several limitations, most notably that other dietary 
factors such as dietary fibre or fat intake were not evaluated by the 
researchers. Also, the design of the study prevented the researchers 
from proving causality.

“These results require replication in future prospective, randomised 
trials using a dietary source of daidzein in women with low oestrogen 
levels, as well as correlative dietary studies to link them to dietary 
habits, including supplement use,” concluded the authors.

CVD causes almost 50 per cent of deaths in Europe, and is reported to 
cost the EU economy an estimated €169bn ($202bn) per year. According to 
the American Heart Association, 34.2 per cent of Americans (70.1m 
people) suffered from some form of cardiovascular disease (CVD) in 2002.
-- 
Kathrynne Holden, MS, RD < fivestar at nutritionucanlivewith.com >
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