This starts by been unexpected and puts everything into question. We
have several related variables in play here and no trustworthy idea
on how to proceed except to become wary of any obvious cause effect
pairing as simply been too simple when the effective operator has
several key elements. Our minds are not trained well to draw the
best conclusions and simple logic draws compelling but wrong answers.
Ouch!
It is one more reminder that biology does not rely on binary logic.
It is too soon even to draw practical conclusions except to keep a
watching brief and to be particularly skeptical regarding cholesterol
claims.
HDL influences
synthesis and absorption of cholesterol
By Antonio Pasolini
12:43 July 12, 2012
Brazilian researchers
have made new discoveries about the relationship between good and bad
cholesterol (pictured) and the former's relationship with insulin
New research carried
out at São Paulo University’s School of Medicine in Brazil reveals
that HDL concentrations in the blood influence the synthesis and
absorption of cholesterol by the body, besides being linked to how
insulin impacts on the metabolism of glucose. HDL, or high-density
lipoprotein, is also commonly referred to as "good cholesterol."
In order to better
understand how HDL works in the human body, a research team led by
Eder C. R. Quintão selected 66 healthy volunteers recruited in the
city of Campinas, in São Paulo state. The group was equally split
between volunteers with low and high plasmatic concentrations of HDL.
The researchers took
care to keep a balance between men and women in both groups, and to
select volunteers of the same age bracket and with normal Body Mass
Index (BMI). They excluded people suffering from diabetes, smokers,
alcohol drinkers and users of medications that alter lipoprotein
metabolism, including contraceptives. They also looked at the eating
habits of the participants. “The more greens a person eats, the
higher the phytosterols in the blood are – the vegetable equivalent
of cholesterol. Since this was one of the markers analyzed in the
study, the participants needed to follow a similar diet to avoid
biased results,” Quintão said.
Data analysis showed
that volunteers from the low HDL group synthesized more cholesterol,
but absorbed less of it through the intestine while high HDL
participants synthesized less cholesterol, but absorbed more through
the intestine. “This data seemed incongruous,” Quintão noted,
“because epidemiological studies show that people who absorb
more cholesterol through the intestine are at a higher risk of having
a heart attack. It is strange that people who absorb more
cholesterol are those with higher HDL,” he said. The team now
intends to start a new research to understand this paradox.
The researchers were
also surprised to find that volunteers with low HDL were less
sensitive to the effect of insulin in comparison to volunteers with
high HDL. They found this out when they related the concentration
of insulin to the glucose found in the bloodstream of people who were
fasting.
“We identified this
process of insulin resistance at a very early stage. They were
healthy people, without symptoms and normal BMI. We don’t know
whether in 10 years’ time there will be more diabetes in this
group. It is a new study pathway,” he said. Existing scientific
literature reinforces the hypothesis that higher concentrations of
HDL improve the absorption of insulin produced in the pancreas during
the metabolism of glucose in peripheral tissue.
Previous studies had
highlighted the important role this lipoprotein plays in the
prevention of cardiovascular diseases and atherosclerosis. Previously
it was believed that HDL’s protective action was linked to its
capacity to remove cholesterol from the walls of arteries and take it
back to the liver, where it would be reused or excreted. “Getting a
better understanding of the role played by HDL in metabolizing
cholesterol is key, because the benefits of raising the levels of
this lipoprotein in the blood outstrips the harm caused by the
elevation of LDL (‘bad cholesterol’),” said Quintão.
He added that current
medication to fight cholesterol acts by reducing LDL and VLDL
concentrations, lipoproteins that also carry cholesterol to the
tissues. But when they cross artery walls they get stuck and
contribute to the formation of atherosclerotic plaque. “It would
be ideal to develop drugs that can boost HDL concentration in the
blood. Diet and exercise have little impact on this process. Regular
alcohol consumption can increase HDL but it can also increase
morbidity for other non-cardiovascular reasons,” Quintão added.
The researchers also
looked at several proteins and enzymes that regulate the production
of HDL.
Details of the
research were published in Clinica Chimica Acta magazine.
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