Nutrition and immunity in children
by Prof Ranjit K Chandra
Nutrition plays a key role in the maintenance of optimal
immune responses of both the young and the old. A balanced diet that supplies adequate
amounts of the essential nutrients strengthens the immune system , whereas over-
and under-nutrition have the opposite effects.
Infants and young children are most susceptible to infections and illnesses and
it's every parent's desire to help their children build a strong immune system so
that they could grow up strong and healthy. So, in terms of nutrition, what can
parents do to achieve that? To address some questions on nutrition and immunity
in children is Prof. Ranjit Kumar Chandra.
Prof. Chandra is the University Research Professor and Director of Allergy/Immunology
at Memorial University of Newfoundland, in St. John's, Canada. He holds appointments
in the Departments of Pediatrics, Medicine, Biochemistry and Gerontology. He is
the first Carnegie Visiting Professor at Johns Hopkins Univeristy since 1992, an
Adjunct Professor at the New York Medical College, and and Honorary Professor at
universities in Beijing, Napoli, Santiago di Chile, and Antiqouia. Prof. Chandra
is the Director of the first and only World Health Organization Centre for Nutritional
Immunology.
Q1. Children are most susceptible to infections during their first
year of life. Why is this so?
A) The newborn starts life with an immature immune system. All aspects of
host defense are less efficient than in the adult and it takes 3-5 years for immune
responses to reach adult levels.
Q2. Some Asian parents still believe that a fat baby is a healthy
baby. This is not true as studies have shown that overweight and obesity may reduce
immunity. Please comment.
A) Just as undernutrition is harmful for immunity, so is overnutrition and
obesity. An obese child has impaired function of polymorphonuclear leukocytes and
cell-mediated immunity . Paradoxically, some of it is due to reduced intake of essential
micronutrients such as iron and zinc.
Q3. Some nutrients such as protein, vitamin B6 and the antioxidants
(Vitamins A, C, E, zinc, selenium and beta-carotene) have demonstrated immunity-boosting
functions. How do they work?
A) There are several mechanisms of action of micronutrients. Many, including
iron and vitamin B6, are essential cofactors of enzymes involved in critical pathways
of metabolism. Others, such as zinc, are cofactors for enzymes involved in DNA synthesis
and therefore cell division and protein synthesis.
Q4. Nutrient excesses, such as dietary fat, iron and vitamin E
are immunosuppressive. What do you mean by excess, in terms of the RDA?
A)The amounts of nutrients that are 'excessive' in relation to the immune
system depends upon the nutrient. For example, fat intake in excess of 30% of total
energy suppresses immune responses. For vitamin E, levels of 400 mg and above are
less efficient than a level of 40-100 mg for the majority of immune responses. An
intake of zinc of 50 mg per day is immunosuppressive and 25 mg a day is the maximum
that should be recommended. The margin of safety for selenium is very small.
Q5. In terms of diet, what's your advice to parents on how they
could boost their infants and children's immunity?
A) There are three key words that I use to define optimum diet for the best
immune function: BALANCE, viz. foods should be derived from all groups including
fruits and vegetables, cereals and grains, dairy products, meats, etc. VARIETY,
viz. within each food group, a variety of foods should be consumed; for example,
several types of fruits and vegetables. And finally, MODERATION; neither too little
nor too much is good for the immune system.
Q6. Younger children suffer more and longer duration of the common
cold than older kids and adults. There have been lots of controversies in terms
of vitamin C's potency in preventing and/or shortening the duration of the common
cold and flu. In your opinion, would a vitamin C-rich diet (lots of fruits) boost
children's immune system and keep colds away?
A)Eating plenty of fruits is good for the immune system. However, the benefits
go beyond the vitamin C content of these foods. Other nutritional components including
flavonoids and phytochemicals are important.
Q7. Would you recommend multi-vitamin/mineral supplements for
children who eat poorly or are finicky in their eating behaviors, to ensure a healthy
immune system? If so, what type and dose of supplements would you recommend for
children? If not, why not?
A)Some children are fussy eaters and in spite of best efforts, they do not eat enough
amount and variety of foods to satisfy the nutritional requirements. There is no
'ideal' multivitamin supplement for boosting immunity in young children as yet.
For older children who can swallow tablets or capsules, an extensively researched
recently marketed preparation can be recommended. It is available as TALISMAN (ARTS
Foundation, P.O. Box 21272, St. John's, NF A1A 5B2, Canada, fax -1-709-753-3322)
or as IMMUNOBOOST (TSAR Health, 126 Qutub Plaza DLF Phase I, Gurgaon 122002, India,
fax -91-124-656 3242).
Q8. Common everyday food such as garlic and onions are said to
boost our immune system. Please comment.
A) Garlic has been shown to improve defenses and reduce the occurrence of
heart disease and cancer. Much of the work has been done on animals but some epidemiological
studies also suggest a similar Benefit for humans, although the data are not conclusive.
Q9 Other factors, such as stress and inadequate sleep can also
take their toll on our immune system. Please elaborate.
A) Physical and mental stress are detrimental to the immune system. Acute and chronic
sleep deprivation impair immune responses. Adults have learnt to reduce stress by
a variety of methods, including yoga and meditation.
Q10. Exercise is said to boost our immune system. Please explain
how it works.
A) Moderate physical exercise increases some immune responses, such as interleukin-2
production, natural killer cell activity and lymphocyte response to mitogens. The
mechanism(s) is not clear