Research Roundtable

Research Roundtable
by Lori Dahm
Vitamin D and prebiotics take center stage.
This year has witnessed increased interest in the nutritional aspects of dairy, with research focused upon identifying the components within dairy and their nutritional benefits.
The Dairy Council of California and Dairy Field hosted
a roundtable discussion on March 28, 2006, in Oakland, Calif., that
highlighted two particular aspects of the dairy picture — vitamin D
and prebiotics — and their health implications, discussed by two of
the industry’s research experts.
Dr. Coni Francis is the scientific affairs manager for
GTC Nutrition, a provider of customized nutrition solutions and
science-based ingredients to the food industry. Before joining the company,
Francis researched glycemia and insulin sensitivity as well as insulin
response at Texas Womens’ University and the University of Colorado
Health Sciences Center.
Francis currently focuses on researching and
communicating the science behind prebiotic fibers and the mechanisms by
which they work. She professes a pragmatic point of view, having been in
the field of diabetics for more than 30 years, and strongly believes that
“today’s consumers are more health-conscious, and although they
will look for nutritionally enhanced foods, they will not sacrifice taste
or convenience.”
Dr. Charles Stephensen is a research scientist with
the U.S. Department of Agriculture Western Human Nutrition Research Center,
(WHNRC), and has been at UC-Davis as an adjunct professor in the nutrition
department for seven years. The WHNRC has 15 research scientists and four
labs that study nutrition and immune function. Stephensen works on
immunology and infectious diseases, and particularly on vitamin A and
immune function. Vitamins A and D are closely related and have similar
mechanisms of action.
Stephensen finds vitamin D very interesting these days
with regard to inflammation, immune function, chronic disease and the way
it acts at the cellular molecular level. “I developed an interest
over the past year in particular on vitamin D and the risk of deficiency in
the U.S.,” he says, “and how that may affect people’s
resistance to infectious disease or response to immunization or risk of
chronic disease.”
The discussion was moderated by Dr. Lori Hoolihan,
research specialist for the Dairy Council of California.
Hoolihan: Dr.
Francis, let’s start with you. Why don’t you give us a bit of
an overview of the basics — what are prebiotics and what are some of
the implications or the importance that they have to the dairy industry?
Francis: Prebiotics are
nondigestible substances that are passed through the stomach and the small
intestine in an intact state. They are then fermented by Bifidiobacteria
and Lactobacilli in the large bowel, which in turn creates short-chain
fatty acids (SCFA) for positive effects on human health. Our gut is
essentially about three pounds of bacteria. Numerous health benefits can be
achieved by modulating these bacteria and encouraging the grown of
beneficial bacteria.
The intention is to nourish the beneficial bacteria to
product SCFAs, which are instrumental in improving health. SCFAs typically
produced are acetate, butyrate and proproinate.
The acetate is metabolized in the muscle and the
kidney and the heart and the brain. The butyrate is the preferred source of
energy from the enterocytes that are in the colon. And also, the butyrate
produced is what is thought to reduce the incidence of cancer and lesions
in the colon, and is therefore often referred to as offering immune
properties in terms of preventing cancer.
Then the proprionate is taken up by the liver, which
may suppress the synthesis of cholesterol — potentially reducing
cholesterol and offering a positive impact in combating heart disease.
In addition, the SCFAs increase the volume of water
and sodium absorption in the colon, so they can provide better digestive
health. Prebiotics are an ideal ingredient for dairy applications because
they acidify the intestinal luminal environment, thus increasing the
absorption of minerals such as and magnesium to improve bone health.
Such benefits cannot be easily achieved by consuming
simple food and beverage products because consumers would have to consume
approximately 22 bananas, 15 onions or 383 garlic cloves to realize the
benefits of offered by certain types of prebiotics.
Hoolihan: Can you talk
about some of the more recent research and the biggest areas that are being
looked at in terms of prebiotic health benefits?
Francis: Digestive
and immune health are the most predominantly studied areas in prebiotics.
One reason is that the gut is the largest immune system within the body.
About 60 or 65 percent of the immunoglobulins that are secreted in the body
end up being secreted into the gut.
An important — but less publicized —
benefit of prebiotic fiber is its ability to significantly improve mineral
absorption. With one of the prebiotic fibers on the market there is the
expression of a calcium binding protein in the large intestine, rather than
just in the small intestine. Therefore you have increased mineral
absorption.
Current research also indicates that prebiotic fiber
may assist in delaying hunger, similar to the viscous fibers on the market.
Prebiotics are much easier to incorporate into applications because they
are very soluble, and are able to retain water in addition to offering
functional benefits such as flavor enhancement and improved texture.
More research is needed on the ability of prebiotics
to offer glycemic health and cholesterol and lipid lowering benefits. Yet
as research continues and improves, it’s very possible that prebiotic
fibers may offer similar heart-health benefits currently being touted by
the use of oat and barley fibers.
Hoolihan: Let’s turn
to Dr. Charles Stephensen. Why don’t you start by giving us an
overview of the vitamin D area and your specific research interests?
Stephensen: One of the
important aspects about vitamin D right now is what our dietary intake
should be. The last dietary guidelines occurred in 1997. There’s been
much research on vitamin D and bone metabolisms, like the prevention of
osteoporosis. Higher vitamin D intake is good for maintaining bone health
and minimizing bone turnover. That’s why vitamin D aligns with
calcium to maintain strong bones and so on. That’s sort of the
central role of vitamin D.
There are other functions of vitamin D in the body
relating to immune function that are not as well understood. There’s
new data that makes nutritionists think that vitamin D may be good for
preventing some chronic diseases that are immune mediated, like autoimmune
disease or preventing development of cancer because of the effects on cell
proliferation. That research is relatively new compared to our knowledge of
vitamin D and bone metabolism. There are a lot of questions about what
benefits may be realized at levels of intake that are higher than what is
needed to prevent deficiency.
In our laboratory we’re actually working on
at the cellular molecular role of nutrients like vitamin A and D affecting
immune function, particularly T cell development. T cells are those cells
in the immune system that help promote a robust response to immunization,
like the flu vaccine. In order to promote a good memory response producing
antibody and that sort of thing, you need healthy, happy T cells, and
vitamin A and vitamin D are important there.
Hoolihan: Vitamin D has
traditionally been linked with calcium absorption and, of course, bone
health. You mentioned immune function, and we’ve also heard of cancer
prevention and more. Which of those do you think have the most promise of
being clinically relevant? Do you have any sense for which of those might
be considered in the development of the next round of dietary guidelines
for D?
Stephensen: Well, the
first thing that’s going to be considered is still bone health,
because there’s a lot more data now than there was in 1997. The
dietary guideline is set so that we take in enough to prevent rickets. But
above the level of preventing rickets, there’s biochemical evidence
that bone health is improved at higher levels of intake.
Hoolihan: So you think
the recommendations will still come back to the research on the bone
health?
Stephensen: Primarily,
because it’s pretty concrete. There’s a lot of good data there.
With regard to the other benefits such as cancer, there are epidemiologic
studies showing that more vitamin D or more sun exposure is associated with
decreased risk of certain cancers, like prostate cancer in men, also to
some extent colon cancer, and also to some extent breast cancer.
Besides bone health and cancer prevention, vitamin D
affects the development and function of cells in the immune system.
There’s a lot unknown there and there’s a lot of potential
benefit.
Vitamin D is of benefit in protection against certain
infectious diseases. Several good studies show that vitamin D deficiency is
associated with risk of tuberculosis. Recent research published in the past
few months shows that one of the key cells that protects against
tuberculosis, macrophage, directly responds to vitamin D.
And actually, vitamin D is required for the normal
synthesis of a particular antibacterial peptide, a small protein
that’s an antibiotic that’s produced by the macrophage. In
order for the macrophage to produce that peptide antibiotic, it needs
vitamin D. And those peptide antibiotics kill organisms like Mycobacterium
tuberculosis. So that’s one example where vitamin D may be key to
prevention of an infectious disease.
Multiple sclerosis is an autoimmune disease where the
body’s own T cells are reacting against antigens in the central
nervous system and basically destroying nerve conduction in the central
nervous system. In animal models, several nutrients, including vitamin D,
seem to have an anti-inflammatory effect. Thus, vitamin D may have a role
in preventing autoimmune diseases like MS by decreasing the inflammation
that causes the disease.
While vitamin D helps macrophages produce some
antibacterial peptides, a key part of the role of vitamin D in the immune
response is that it may help the immune system to regulate itself. So when
you’re sort of done with the infection and the pathogenic organism is
cleared, the immune system then need to down-regulate itself. And this sort
of regulatory role of vitamin D may play that sort of role with regard to
helping prevent or diminish severity of diseases like multiple sclerosis in
animal models. And there’s epidemiologic data that suggests the
better vitamin D status you have early in life, the lower risk of multiple
sclerosis later in life.
There’s similar data for juvenile onset
diabetes, which is also an autoimmune disease. Better vitamin D status
early in life may protect against development of autoimmune diabetes.
Hoolihan: What is the
possibility of the vitamin D recommendations being increased in the next
few years?
Stephensen: Well,
certainly in the vitamin D research community there are many advocates of
that, particularly regarding bone health. The bigger potential right now
are these other health benefits, like cancer and autoimmune disease, but
there’s not enough data yet to convince the dietary guidelines
committee of an actual health benefit from the data. But there is data on
bone metabolism, which will drive the discussion.
With regard to some of these other health benefits,
there was one study published recently on perhaps the most common
infectious disease in the U.S. Two-thirds of American adults have
gingivitis, a bacterial infection of your gums. This study showed that the
higher vitamin D intake you have, the lower your risk of gingivitis and the
less severe gingivitis you have. The same antibacterial peptides and
regulatory mechanisms that I talked about with regard to tuberculosis and
autoimmune disease are at play in your mouth every day affecting
development of gingivitis. So that’s an area and an example of how it
might have a somewhat common health benefit for a lot of people.
Francis: I think it is
kind of interesting that these two things parallel each other. Prebiotic
fibers do not provide any food for the bacteria in the mouth, so this
ingredient can be used as part of a sweetening mechanism for
anti-cariogenic products.
Hoolihan: So D and
prebiotics for gingivitis.
Stephensen: In a smoothie
preferably.
Hoolihan: A perfect
connection.
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