How to boost your immune system

What can you do?
On the whole, your immune system does a remarkable job
of defending you against disease-causing microorganisms.
But sometimes it fails: A germ invades successfully and
makes you sick. Is it possible to intervene in this process
and make your immune system stronger? What if you
improve your diet? Take certain vitamins or herbal
preparations? Make other lifestyle changes in the hope of
producing a near-perfect immune response?
The idea of boosting your immunity is enticing, but the
ability to do so has proved elusive for several reasons. The
immune system is precisely that — a system, not a single
entity. To function well, it requires balance and harmony.
There is still much that researchers don’t know about the
intricacies and interconnectedness of the immune response.
For now, there are no scientifically proven direct links
between lifestyle and enhanced immune function.
But that doesn’t mean the effects of lifestyle on the immune
system aren’t intriguing and shouldn’t be studied. Quite a
number of researchers are exploring the effects of diet,
exercise, age, psychological stress, herbal supplements, and
other factors on the immune response, both in animals and
in humans. Although interesting results are emerging, thus
far they can only be considered preliminary. That’s because
researchers are still trying to understand how the immune
system works and how to interpret measurements of
immune function. The following sections summarize some
of the most active areas of research into these topics. In the
meantime, general healthy-living strategies are a good way
to start giving your immune system the upper hand.
Adopt healthy-living strategies
Your first line of defense is to choose a healthy lifestyle.
Following general good-health guidelines is the single best
step you can take toward keeping your immune system
strong and healthy. Every part of your body, including your
immune system, functions better when protected from
environmental assaults and bolstered by healthy-living
strategies such as these:
Don’t smoke.
Eat a diet high in fruits, vegetables, and whole grains,
and low in saturated fat.
Exercise regularly.
Maintain a healthy weight.
Control your blood pressure.
If you drink alcohol, drink only in moderation.
Get adequate sleep.
Take steps to avoid infection, such as washing your hands
frequently and cooking meats thoroughly.
Get regular medical screening tests for people in your age
group and risk category.
Be skeptical
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 the 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 kinds of cells the immune system needs to function
at its optimum level.
Scientists do know more about the low end of the scale.
When the number of T cells in an HIV/AIDS patient drops
below a certain level, the patient gets sick because the
immune system doesn’t have enough T cells to fight off
infection. So there is a bottom number below which the
immune system can’t do its job. But how many T cells is
comfortably enough, and beyond that point, is more better?
We don’t know.
Many researchers are trying to explore the effects of a
variety of factors — from foods and herbal supplements to
exercise and stress — on immunity. Some take measures of
certain blood components like lymphocytes or cytokines.
But thus far, no one really knows what these measurements
mean in terms of your body’s ability to fight disease. They
provide a way of detecting whether something is going on,
but science isn’t yet sufficiently advanced to understand
how this translates into success in warding off disease.
A different scientific approach looks at the effect of certain
lifestyle modifications on the incidence of disease. If a study
shows significantly less disease, researchers consider
whether the immune system is being strengthened in some
way. Based on these studies, there is now evidence that
even though we may not be able to prove a direct link
between a certain lifestyle and an improved immune
response, we can at least show that some links are likely.

Age and immunity
Earlier in this report (see “Cancer: Missed cues”), we noted
that one active area of research is how the immune system
functions as the body ages. Researchers believe that the
aging process somehow leads to a reduction of immune
response capability, which in turn contributes to more
infections, more inflammatory diseases, and more cancer.
As life expectancy in developed countries has increased, so
too has the incidence of age-related conditions. Happily,
investigation into the aging process can benefit us all — no
matter what our age.
While some people age healthily, the conclusion of many
studies is that, compared with younger people, the elderly
are far more likely to contract infectious diseases.
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.
Thymus function declines beginning at age 1; 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.
Researchers at the University of Arkansas are looking at
another aspect of why the immune system seems to
weaken with age. They studied cell death in mice. They
conducted an experiment to compare the lifespan of
memory T lymphocytes in older mice with those of younger
mice and found that the lymphocytes in older mice die
sooner. This suggests that as the lymphocytes die off, the
elderly immune system loses its memory for the microbes it
is intended to fight and fails to recognize the microbes when
they reappear. The body thus becomes less able to mount a
vigorous immune response.
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, vaccine effectiveness was 23%,
whereas for healthy children (over age 2), it was 38%. 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
nonvaccination.
Yet other researchers are looking at the 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.
What about diet?
Like any fighting force, the immune system army marches
on its stomach. 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 are studies of the effects of nutritional changes on the
immune systems of animals, but again there are few
studies that address the development of diseases in animals
as a result of changes in immunity. For example, one group
of investigators has found that in mice, diets deficient in
protein reduce both the numbers and function of T cells and
macrophages and also reduce the production of
immunoglobulin A (IgA) antibody.
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. But the research at this stage is promising, at
least for some of the micronutrients.
So what can you do? If you suspect your diet is not
providing you with all your micronutrient needs — maybe
you don’t like vegetables or you choose white bread over
whole grains — taking a daily multivitamin and mineral
supplement brings health benefits of many types, beyond
any possibly beneficial effects on the immune system.
Taking megadoses of a single vitamin does not. More is not
necessarily better. Researchers are investigating the
immune boosting potential of a number of different
nutrients.
Selenium. Some studies have suggested that people with
low selenium levels are at greater risk of bladder, breast,
colon, rectum, lung, and prostate cancers. A large-scale,
multiyear study is currently in progress to look at the effects
of combining selenium and vitamin E on prostate cancer
prevention.
Vitamin A. Experts have long known that vitamin A plays a
role in infection and maintaining mucosal surfaces by
influencing certain subcategories of T cells and B cells and
cytokines. Vitamin A deficiency is associated with impaired
immunity and increased risk of infectious disease. On the
other hand, according to one study, supplementation in the
absence of a deficiency didn’t enhance or suppress T cell
immunity in a group of healthy seniors.
Vitamin B2. There is some evidence that vitamin B2
enhances resistance to bacterial infections in mice, but
what that means in terms of enhancing immune response is
unclear.
Vitamin B6. Several studies have suggested that a vitamin
B6 deficiency can depress aspects of the immune response,
such as lymphocytes’ ability to mature and spin off into
various types of T and B cells. Supplementing with
moderate doses to address the deficiency restores immune
function, but megadoses don’t produce additional benefits.
And B6 may promote the growth of tumors.
Vitamin C. The jury is still out on vitamin C and the immune
system. Many studies have looked at vitamin C in general;
unfortunately, many of them were not well designed.
Vitamin C may work in concert with other micronutrients
rather than providing benefits alone.
Vitamin D. For many years doctors have known that people
afflicted with tuberculosis responded well to sunlight. An
explanation may now be at hand. Researchers have found
that vitamin D, which is produced by the skin when exposed
to sunlight, signals an antimicrobial response to the
bacterium responsible for tuberculosis, Mycobacterium
tuberculosis . Whether vitamin D has similar ability to fight
off other diseases and whether taking vitamin D in
supplement form is beneficial are questions that need to be
resolved with further study.
Vitamin E. A study involving healthy subjects over age 65
has shown that increasing the daily dose of vitamin E from
the recommended dietary allowance (RDA) of 30 mg to 200
mg increased antibody responses to hepatitis B and tetanus
after vaccination. But these increased responses didn’t
happen following administration of diphtheria and
pneumococcal vaccines.
Zinc. Zinc is a trace element essential for cells of the
immune system, and zinc deficiency affects the ability of T
cells and other immune cells to function as they should.
Caution: While it’s important to have sufficient zinc in your
diet (15–25 mg per day), too much zinc can inhibit the
function of the immune system.
Herbs and other 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.
But that doesn’t mean we should discount the benefits of all
herbal preparations. Everyone’s immune system is unique.
Each person’s physiology responds to active substances
differently. So if your grandmother says she’s been using
an herbal preparation for years that protects her from
illness, who’s to say that it doesn’t? The problem arises
when scientists try to study such a preparation among large
numbers of people. The fact that it works for one person
won’t show up in the research data if it’s not doing the
same for a larger group.
Scientists have looked at a number of herbs and vitamins in
terms of their potential to influence the immune system in
some way. Much of this research has focused on the
elderly, children, or people with compromised immune
systems, such as AIDS patients. And many of the studies
have had design flaws, which means further studies are
needed to confirm or disprove the results. Consequently,
these findings should not be considered universally
applicable.
Some of the supplements that have drawn attention from
researchers are these:
Aloe vera. For now, there’s no evidence that aloe vera can
modulate immune response. Because many different
formulations and compounds have been used in studies,
comparing the results is difficult. However, there is some
evidence that topical aloe vera is helpful for minor burns,
wounds, or frostbite, and also for skin inflammations when
combined with hydrocortisone. Studies have found aloe vera
is not the best option for treating breast tissue after
radiation therapy.
Astragalus membranes. The astragalus product, which is
derived from the root of the plant, is marketed as an
immune-system stimulant, but the quality of the studies
demonstrating the immune-stimulating properties of
astragalus are poor. Furthermore, it may be dangerous.
Echinacea. An ocean of ink has been spilled extolling
echinacea as an “immune stimulant,” usually in terms of its
purported ability to prevent or limit the severity of colds.
Most experts don’t recommend taking echinacea on a long-
term basis to prevent colds. A group of physicians from
Harvard Medical School notes that studies looking at the
cold prevention capabilities of echinacea have not been well
designed, and other claims regarding echinacea are as yet
not proven. Echinacea can also cause potentially serious
side effects. People with ragweed allergies are more likely
to have a reaction to echinacea, and there have been cases
of anaphylactic shock. Injected echinacea in particular has
caused severe reactions. A well-designed study by
pediatricians at the University of Washington in Seattle
found echinacea didn’t help with the duration and severity of
cold symptoms in a group of children. A large 2005 study of
437 volunteers also found that echinacea didn’t affect the
rate of cold infections or the progress and severity of a cold.
Garlic. Garlic may have some infection-fighting capability. In
laboratory tests, researchers have seen garlic work against
bacteria, viruses, and fungi. Although this is promising,
there haven’t been enough well-designed human studies
conducted to know whether this translates into human
benefits. One 2006 study that looked at rates for certain
cancers and garlic and onion consumption in southern
European populations found an association between the
frequency of use of garlic and onions and a lower risk of
some common cancers. Until more is known, however, it’s
too early to recommend garlic as a way of treating or
preventing infections or controlling cancer.
Ginseng. It’s not clear how the root of the ginseng plant
works, but claims on behalf of Asian ginseng are many,
including its ability to stimulate immune function. Despite
the claims of a number of mainly small studies, the National
Center for Complementary and Alternative Medicine
(NCCAM) considers there have been insufficient large
studies of a high enough quality to support the claims.
NCCAM is currently supporting research to understand
Asian ginseng more fully.
Glycyrrhiza glabra (licorice root). Licorice root is used in
Chinese medicine to treat a variety of illnesses. Most
studies of licorice root have been done in combination with
other herbs, so it’s not possible to verify whether any effects
were attributable to licorice root per se. Because of the
potential side effects of taking licorice and how little is
known about its benefits — if any — for stimulating immune
function, this is an herb to avoid.
Probiotics. There are hundreds of different species of
bacteria in your digestive tract, which do a bang-up job
helping you digest your food. Now researchers, including
some at Harvard Medical School, are finding evidence of a
relationship between such “good” bacteria and the immune
system. For instance, it is now known that certain bacteria
in the gut influence the development of aspects of the
immune system, such as correcting deficiencies and
increasing the numbers of certain T cells. Precisely how the
bacteria interact with the immune system components isn’t
known. As more and more intriguing evidence comes in to
support the link that intestinal bacteria bolster the immune
system, it’s tempting to think that more good bacteria would
be better. At least, this is what many marketers would like
you to believe as they tout their probiotic products.
Probiotics are good bacteria, such as Lactobacillus and
Bifidobacterium, that can safely dwell in your digestive tract.
You’ll now find probiotics listed on the labels of dairy
products, drinks, cereals, energy bars, and other foods.
Ingredients touted as “prebiotics,” which claim to be
nutrients that feed the good bacteria, are also cropping up in
commercially marketed foods. Unfortunately, the direct
connection between taking these products and improving
immune function has not yet been made. Nor has science
shown whether taking probiotics will replenish the good
bacteria that get knocked out together with “bad” bacteria
when you take antibiotics.
Another caution is that the quality of probiotic products is
not consistent. Some contain what they say they do; some
do not. In a 2006 report, the American Academy of
Microbiology said that “at present, the quality of probiotics
available to consumers in food products around the world is
unreliable.” In the same vein, the FDA monitors food
packages to make sure they don’t carry labels that claim the
products can cure diseases unless the companies have
scientific evidence to support the claims. Does this mean
taking probiotics is useless? No. It means the jury is still
out on the expansive health claims. In the meantime, if you
choose to take a probiotic in moderation, it probably won’t
hurt, and the scientific evidence may ultimately show some
benefit.
The stress connection
Modern medicine, which once treated the connection
between emotions and physical health with skepticism, 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. But although the relationship
between stress and immune function is being studied by a
number of different types of scientists, so far it is not a
major area of research for immunologists.
Studying the relationship between stress and the immune
system presents difficult challenges. 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 who repeat the
same experiment many times with many different animals
or human beings, and who get the same result most of the
time, hope that they can draw reasonable conclusions.
Some researchers place animals into stressful situations,
such as being trapped in a small space or being placed near
an aggressive animal. Different functions of their immune
systems, and their health, are then measured under such
stressful conditions. On the basis of such experiments,
some published studies have made the following claims:
Experimentally created “stressful” situations delayed the
production of antibodies in mice infected with influenza
virus and suppressed the activity of T cells in animals
inoculated with herpes simplex virus.
Social stress can be even more damaging than physical
stress. For example, some mice were put into a cage with a
highly aggressive mouse two hours a day for six days and
repeatedly threatened, but not injured, by the aggressive
mouse — a “social stress.” Other mice were kept in tiny
cages without food and water for long periods — a “physical
stress.” Both groups of mice were exposed to a bacterial
toxin, and the socially stressed animals were twice as likely
to die.
Isolation can also suppress immune function. Infant
monkeys separated from their mothers, especially if they
are caged alone rather than in groups, generate fewer
lymphocytes in response to antigens and fewer antibodies
in response to viruses.
Many researchers report that stressful situations can reduce
various aspects of the cellular immune response. A
research team from Ohio State University that has long
worked in this field suggests that psychological stress
affects the immune system by disrupting communication
between the nervous system, the endocrine (hormonal)
system, and the immune system. These three systems
“talk” to one another using natural chemical messages, and
must work in close coordination to be effective. The Ohio
State research team speculates that long-term stress
releases a long-term trickle of stress hormones — mainly
glucocorticoids. These hormones affect the thymus, where
lymphocytes are produced, and inhibit the production of
cytokines and interleukins, which stimulate and coordinate
white blood cell activity. This team and others have reported
the following results:
Elderly people caring for relatives with Alzheimer’s disease
have higher than average levels of cortisol, a hormone
secreted by the adrenal glands and, perhaps because of the
higher levels of cortisol, make fewer antibodies in response
to influenza vaccine.
Some measures of T cell activity have been found to be
lower in depressed patients compared with nondepressed
patients, and in men who are separated or divorced
compared with men who are married.
In a year-long study of people caring for husbands or wives
with Alzheimer’s disease, changes in T cell function were
greatest in those who had the fewest friends and least
outside help.
Four months after the passage of Hurricane Andrew in
Florida, people in the most heavily damaged neighborhoods
showed reduced activity in several immune system
measurements. Similar results were found in a study of
hospital employees after an earthquake in Los Angeles.
In all of these studies, however, there was no proof that the
immune system changes measured had any clear adverse
effects on health in these individuals.

Does being cold make you sick?
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. They’ve found that
exposure to cold does increase levels of some cytokines,
the proteins and hormones that act as messengers in the
immune system, but how this affects health isn’t clear.
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: Good or bad for 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 maintain a healthy immune
system? 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 such as cytokines, white blood cells, and
certain antibodies. While some changes have been
recorded, immunologists do not yet know what these
changes mean in terms of human immune response. No
one yet knows, for example, whether an increase in
cytokines is helpful or has any true effect on immune
response. Similarly, no one knows whether a general
increase in white cell count is a good thing or a bad thing.
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.