Many
products on store shelves claim to boost or support immunity.
But the concept of boosting immunity actually makes little sense
scientifically. In fact, boosting the number of cells in your
body — immune cells or others — is not necessarily
a good thing. For example, athletes who engage in "blood
doping" — pumping blood into their systems to boost
their number of blood cells and enhance their performance —
run the risk of strokes.
Attempting
to boost the cells of your immune system is especially complicated
because there are so many different kinds of cells in the immune
system that respond to so many different microbes in so many
ways. Which cells should you boost, and to what number? So far,
scientists do not know the answer. What is known is that the
body is continually generating immune cells. Certainly it produces
many more lymphocytes than it can possibly use. The extra cells
remove themselves through a natural process of cell death called
apoptosis — some before they see any action, some after
the battle is won. No one knows how many cells or what the best
mix of cells the immune system needs to function at its optimum
level.
IMMUNE
SYSTEM AND AGE
As
we age, our immune response capability becomes reduced, which
in turn contributes to more infections and more cancer. As life
expectancy in developed countries has increased, so too has
the incidence of age-related conditions.
While
some people age healthily, the conclusion of many studies is
that, compared with younger people, the elderly are more likely
to contract infectious diseases and, even more importantly,
more likely to die from them. Respiratory infections, influenza,
and particularly pneumonia are a leading cause of death in people
over 65 worldwide. No one knows for sure why this happens, but
some scientists observe that this increased risk correlates
with a decrease in T cells, possibly from the thymus atrophying
with age and producing fewer T cells to fight off infection.
Whether this decrease in thymus function explains the drop in
T cells or whether other changes play a role is not fully understood.
Others are interested in whether the bone marrow becomes less
efficient at producing the stem cells that give rise to the
cells of the immune system.
A
reduction in immune response to infections has been demonstrated
by older people's response to vaccines. For example, studies
of influenza vaccines have shown that for people over age 65,
the vaccine is much less effective compared to healthy children
(over age 2). But despite the reduction in efficacy, vaccinations
for influenza and S. pneumoniae have significantly lowered the
rates of sickness and death in older people when compared with
no vaccination.
There
appears to be a connection between nutrition and immunity in
the elderly. A form of malnutrition that is surprisingly common
even in affluent countries is known as "micronutrient malnutrition."
Micronutrient malnutrition, in which a person is deficient in
some essential vitamins and trace minerals that are obtained
from or supplemented by diet, can be common in the elderly.
Older people tend to eat less and often have less variety in
their diets. One important question is whether dietary supplements
may help older people maintain a healthier immune system. Older
people should discuss this question with a physician who is
well versed in geriatric nutrition, because while some dietary
supplementation may be beneficial for older people, even small
changes can have serious repercussions in this age group.
DIET
AND YOUR IMMUNE SYSTEM
Like
any fighting force, the immune system army marches on its stomach.
Healthy immune system warriors need good, regular nourishment.
Scientists have long recognized that people who live in poverty
and are malnourished are more vulnerable to infectious diseases.
Whether the increased rate of disease is caused by malnutrition's
effect on the immune system, however, is not certain. There
are still relatively few studies of the effects of nutrition
on the immune system of humans, and even fewer studies that
tie the effects of nutrition directly to the development (versus
the treatment) of diseases.
There
is some evidence that various micronutrient deficiencies —
for example, deficiencies of zinc, selenium, iron, copper, folic
acid, and vitamins A, B6, C, and E — alter immune responses
in animals, as measured in the test tube. However, the impact
of these immune system changes on the health of animals is less
clear, and the effect of similar deficiencies on the human immune
response has yet to be assessed.
So
what can you do? If you suspect your diet is not providing you
with all your micronutrient needs — maybe, for instance,
you don't like vegetables — taking a daily multivitamin
and mineral supplement may bring other health benefits, beyond
any possibly beneficial effects on the immune system. Taking
megadoses of a single vitamin does not. More is not necessarily
better.
IMPROVE
IMMUNITY WITH HERBS AND SUPPLEMENTS?
Walk
into a store, and you will find bottles of pills and herbal
preparations that claim to "support immunity" or otherwise
boost the health of your immune system. Although some preparations
have been found to alter some components of immune function,
thus far there is no evidence that they actually bolster immunity
to the point where you are better protected against infection
and disease. Demonstrating whether an herb — or any substance,
for that matter — can enhance immunity is, as yet, a highly
complicated matter. Scientists don't know, for example, whether
an herb that seems to raise the levels of antibodies in the
blood is actually doing anything beneficial for overall immunity.
STRESS
AND IMMUNE FUNCTION
Modern
medicine has come to appreciate the closely linked relationship
of mind and body. A wide variety of maladies, including stomach
upset, hives, and even heart disease, are linked to the effects
of emotional stress. Despite the challenges, scientists are
actively studying the relationship between stress and immune
function.
For
one thing, stress is difficult to define. What may appear to
be a stressful situation for one person is not for another.
When people are exposed to situations they regard as stressful,
it is difficult for them to measure how much stress they feel,
and difficult for the scientist to know if a person's subjective
impression of the amount of stress is accurate. The scientist
can only measure things that may reflect stress, such as the
number of times the heart beats each minute, but such measures
also may reflect other factors.
Most
scientists studying the relationship of stress and immune function,
however, do not study a sudden, short-lived stressor; rather,
they try to study more constant and frequent stressors known
as chronic stress, such as that caused by relationships with
family, friends, and co-workers, or sustained challenges to
perform well at one's work. Some scientists are investigating
whether ongoing stress takes a toll on the immune system.
But
it is hard to perform what scientists call "controlled
experiments" in human beings. In a controlled experiment,
the scientist can change one and only one factor, such as the
amount of a particular chemical, and then measure the effect
of that change on some other measurable phenomenon, such as
the amount of antibodies produced by a particular type of immune
system cell when it is exposed to the chemical. In a living
animal, and especially in a human being, that kind of control
is just not possible, since there are so many other things happening
to the animal or person at the time that measurements are being
taken.
Despite
these inevitable difficulties in measuring the relationship
of stress to immunity, scientists are making progress.
DOES
BEING COLD WEAKEN THE IMMUNE SYSTEM?
Almost
every mother has said it: "Wear a jacket or you'll catch
a cold!" Is she right? So far, researchers who are studying
this question think that normal exposure to moderate cold doesn't
increase your susceptibility to infection. Most health experts
agree that the reason winter is "cold and flu season"
is not that people are cold, but that they spend more time indoors,
in closer contact with other people who can pass on their germs.
But
researchers remain interested in this question in different
populations. Some experiments with mice suggest that cold exposure
might reduce the ability to cope with infection. But what about
humans? Scientists have dunked people in cold water and made
others sit nude in subfreezing temperatures. They've studied
people who lived in Antarctica and those on expeditions in the
Canadian Rockies. The results have been mixed. For example,
researchers documented an increase in upper respiratory infections
in competitive cross-country skiers who exercise vigorously
in the cold, but whether these infections are due to the cold
or other factors — such as the intense exercise or the
dryness of the air — is not known.
A group
of Canadian researchers that has reviewed hundreds of medical
studies on the subject and conducted some of its own research
concludes that there's no need to worry about moderate cold
exposure — it has no detrimental effect on the human immune
system. Should you bundle up when it's cold outside? The answer
is "yes" if you're uncomfortable, or if you're going
to be outdoors for an extended period where such problems as
frostbite and hypothermia are a risk. But don't worry about
immunity.
EXERCISE
AND IMMUNITY
Regular
exercise is one of the pillars of healthy living. It improves
cardiovascular health, lowers blood pressure, helps control
body weight, and protects against a variety of diseases. But
does it help to boost your immune system naturally and keep
it healthy? Just like a healthy diet, exercise can contribute
to general good health and therefore to a healthy immune system.
It may contribute even more directly by promoting good circulation,
which allows the cells and substances of the immune system to
move through the body freely and do their job efficiently.
Some
scientists are trying to take the next step to determine whether
exercise directly affects a person's susceptibility to infection.
For example, some researchers are looking at whether extreme
amounts of intensive exercise can cause athletes to get sick
more often or somehow impairs their immune function. To do this
sort of research, exercise scientists typically ask athletes
to exercise intensively; the scientists test their blood and
urine before and after the exercise to detect any changes in
immune system components. While some changes have been recorded,
immunologists do not yet know what these changes mean in terms
of human immune response.
But
these subjects are elite athletes undergoing intense physical
exertion. What about moderate exercise for average people? Does
it help keep the immune system healthy? For now, even though
a direct beneficial link hasn't been established, it's reasonable
to consider moderate regular exercise to be a beneficial arrow
in the quiver of healthy living, a potentially important means
for keeping your immune system healthy along with the rest of
your body.
One
approach that could help researchers get more complete answers
about whether lifestyle factors such as exercise help improve
immunity takes advantage of the sequencing of the human genome.
This opportunity for research based on updated biomedical technology
can be employed to give a more complete answer to this and similar
questions about the immune system. For example, microarrays
or "gene chips" based on the human genome allow scientists
to look simultaneously at how thousands of gene sequences are
turned on or off in response to specific physiological conditions
— for example, blood cells from athletes before and after
exercise. Researchers hope to use these tools to analyze patterns
in order to better understand how the many pathways involved
act at once.
