 General requirements
Adequate nutritional intake is required to maintain health and prevent
disease. Certain nutrients are essential; without them a deficiency
disease will result. Required nutrients that cannot be synthesized by the
body and therefore must be taken regularly are essential amino acids,
water-soluble and fat-soluble vitamins, minerals, and essential fatty
acids. The U.S. Recommended Dietary Allowances (RDAs), one of many sets of
recommendations put out by various countries and organizations, have been
established for these essential nutrients by the Food and Nutrition Board
of the National Academy of Sciences (Table 5). These RDAs are guidelines
and not absolute minimums. Intake of less than the RDA for a given
nutrient increases the risk of inadequate intake and a deficiency
disorder. Nutritional requirements are greater during the periods of rapid
growth (infancy, childhood, and adolescence) and during pregnancy and
lactation. Requirements vary with physical activity, aging, infections,
medications, metabolic disorders (e.g., hyperthyroidism), and other
medical situations. RDAs do not address all circumstances and are designed
only for the average healthy person. Protein, needed to maintain body function and structure, consists of nine
essential amino acids that must be provided from different foods in a
mixed diet. Ten to 15 percent of calories should come from protein. The
oxidation of 1 gram (0.036 ounce) of protein provides 4 kilocalories of
energy. The same is true for carbohydrate, but fat yields 9 kilocalories.
Carbohydrate provides about 45 percent of calories in the American diet,
in the form of sugars, starches (complex carbohydrates), and dietary fibre
(indigestible carbohydrates). Fibre is not digestible but increases the
bulk of the stool and facilitates faster intestinal transit, which some
believe reduces the risk of colon cancer by diminishing the time that
cancer-producing substances in the diet remain in contact with the bowel
wall. Increasing bulk also decreases the concentration of these
substances. Dietary fibre can be insoluble (wheat bran) or soluble (oat
bran and psyllium). Only the soluble fibres found in oats, fruit, and
legumes lower blood cholesterol and benefit individuals with diabetes by
delaying the absorption of glucose.
The most concentrated source of energy is fat, the source of fat-soluble
vitamins and essential fatty acids. Thirty-seven percent of calories in
the American diet come from fat, but the ideal is closer to 30 percent.
The average American diet also contains 450 milligrams daily of
cholesterol, but less than 300 milligrams is recommended. The recommended
daily diet as determined by the U.S. Department of Agriculture is called
the Food Guide Pyramid and consists of 6 to 11 servings of bread, cereal,
rice, or pasta; 3 to 5 servings of vegetables; 2 to 4 servings of fruit; 2
to 3 servings of fish, meat, poultry, dry beans, eggs, or nuts; and 2 to 3
servings of milk, yogurt, or cheese.
Requirements in infancy
Nutritional needs are greatest during the first year of life. Meeting the
energy demands during this period of rapid growth requires 100 to 120
kilocalories per kilogram per day. Breast milk, the ideal food, is not
only readily available at the proper temperature, it also contains
antibodies from the mother that help protect against disease. Infant
formulas closely approximate the contents of breast milk, and both contain
about 50 percent of calories from carbohydrate, 40 percent from fat, and
10 percent from protein. Exclusive Breast milk is recommended for the first six months
of life and may be continued through the first year. Solid foods are
introduced at six months of age starting with rice cereal and then
introducing a new vegetable, fruit, or meat each week. Cow's milk should
not be given to infants younger than six months of age, and low-fat milk
should be avoided throughout infancy because it does not contain adequate
calories and polyunsaturated fats required for development. Additional
iron and vitamins should be given, especially to infants at high risk of
iron deficiency, such as those with a low birth weight.
Toddlers are usually picky eaters, but attempts should be made to include
the following four basic food groups in their diet: meat, fish, poultry,
or eggs; dairy products such as milk or cheese; fruits and vegetables; and
cereals, rice, or potatoes. Mealtime presents an excellent opportunity for
social interaction and strengthening of the family unit. This starts with
the bonding between mother and child during breast-feeding and continues
as a source of family interaction throughout childhood.
Requirements in adolescence
Nutritional needs during adolescence vary according to activity levels,
with some athletes requiring an extremely high-calorie diet. Other
adolescents, however, who are relatively sedentary consume calories in
excess of their energy needs and become obese. Peer pressure and the
desire for social acceptance can profoundly affect the quality of
nutrition of the adolescent as food intake may shift from the home to
fast-food establishments. Pregnancy during adolescence can present special
hazards if the pregnancy occurs before the adolescent has finished growing
and if she has established poor eating habits. Pregnancy increases the
already high requirements for calcium, iron, and vitamins in these
teenagers.
Eating disorders such as anorexia nervosa and bulimia arise predominantly
in young women as a result of biological, psychological, and social
factors. An excessive concern with body image and a fear of becoming fat
are hallmarks of these conditions. The patient with anorexia nervosa has a
distorted body image and an inordinate fear of gaining weight;
consequently she reduces her nutritional intake below the amount needed to
maintain a normal minimal weight. Severe electrolyte disturbances and
death can result. Bulimia is a behavioral disorder marked by binge eating
followed by acts of purging (e.g., self-induced vomiting, ingestion of
laxatives or diuretics, or vigorous exercising) to avoid weight gain.
Requirements of the elderly
The elderly often have decreased intestinal motility and decreased gastric
acid secretion that can lead to nutritional deficiencies. The problem can
be accentuated by poorly fitting dentures, poor appetite, and a decreased
sense of taste and smell. Although lower levels of activity reduce the
need for calories, older persons may feel something is wrong if they do
not have the appetite of their younger years, even if caloric intake is
adequate to maintain weight. The reduction in gastric acid secretion can
lead to decreased absorption of vitamins and other nutrients. Nutritional
deficiencies can reduce the level of cognitive functioning. Vitamin
supplementation, especially with cobalamin (vitamin B12), may be
particularly valuable in the elderly. The diet of the geriatric population
is often deficient in calcium and iron, with the average woman ingesting
only half the amount of calcium needed daily. Decreased intake of
vegetables can also contribute to various nutritional deficiencies.
Constipation, which is common in the elderly, results from decreased
intestinal motility and immobility and is worsened by reduced fluid and
fibre intake. The multiple medications that the elderly are likely to be
taking may contribute to constipation and prevent the absorption of
certain nutrients. Some drugs, such as the phenothiazines, may interfere
with temperature regulation and lead to problems during hot weather,
especially if fluid intake is inadequate.
Requirements in pregnancy
The growing fetus depends on the mother for all nutrition and increases
the mother's usual demand for certain substances such as iron, folic acid,
and calcium, which should be added as supplements to a balanced diet that
contains most of the other required nutrients. The diet of adolescent
girls, however, is often deficient in calcium, iron, and vitamins. If poor
nutritional habits have been established previously and are maintained
during pregnancy, the pregnant adolescent and her fetus are at increased
risk. In addition to avoiding junk foods, the pregnant woman should
abstain from alcohol, smoking, and illicit drugs because these all have a
detrimental effect on the fetus. Although the average recommended weight
gain during pregnancy is approximately 11.3 kilograms (25 pounds), the
pregnant woman should be less concerned with a maximum weight gain than
she is with meeting the nutritional requirements of pregnancy. Low weight
gain (less than 9.1 kilograms) has been associated with intrauterine
growth retardation and prematurity in the United States.
Women who are breast-feeding should continue taking vitamin supplements
and increasing their intake of calcium and protein to provide adequate
breast milk. This regimen will not interfere with the mother's ability to
slowly lose the weight gained during pregnancy.
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Global Burden of Infectious
diseases
Newsletters
|
 Measles
Encyclopædia Britannica Article
Also called rubeola contagious disease caused by a virus, with community
outbreaks taking place about every two to four years. Measles is commonest
in children but may appear in older persons who have escaped it earlier in
life. Infants are immune up to four or five months of age if the mother
has had the disease. Immunity to measles following an attack is usually
lifelong.Measles is so highly communicable that the slightest contact with an
active case may infect a susceptible person. Infectivity is greatest just
before the eruption appears and subsides as the rash fades. Uncomplicated
measles is seldom fatal; deaths attributed to measles usually result from
secondary bronchopneumonia caused by bacterial organisms entering the
inflamed bronchial tree.
After an incubation period of about 10 days, the patient develops fever,
redness and watering of the eyes, profuse nasal discharge, and congestion
of the mucous membranes of the nose and throat—symptoms often mistaken for
those of a severe cold. This period of invasion lasts for 48 to 96 hours.
The fever increases with appearance of a blotchy rash, and the temperature
may rise as high as 104° to 106° F (about 40° C) when the rash reaches its
maximum. Twenty-four to 36 hours before the rash develops, there appear in
the mucous membranes of the mouth typical maculae, called Koplik
spots—bluish-white specks surrounded by bright red areas about 1/32 inch
(0.75 millimetre) in diameter. After a day or two the rash becomes a
deeper red and gradually fades, the temperature drops rapidly, and the
catarrhal symptoms disappear.
Measles must be differentiated from other disorders accompanied by an
eruption. In roseola infantum, a disease seen in babies, a measles-like
rash appears after the child has had a high temperature for two or three
days, but there is no fever at the time of the rash. German measles
(rubella) can be superficially differentiated from measles by the shorter
course of the disease and mildness of the symptoms. Sometimes the rashes
of scarlet fever, serum reactions, and other conditions may, on certain
parts of the body, look like measles. Drugs that may produce rashes
similar to measles are phenobarbital, diphenylhydantoin, the sulfonamides,
phenolphthalein, and penicillin.
Mortality caused by measles declined steadily in the 20th century as the
health of children and infants improved and effective treatment of
complications became possible through the use of sulfonamide and
antibiotic drugs. No drug is effective against measles; the only treatment
required is rest in bed, protection of the eyes, care of the bowels, and
sometimes steam inhalations to relieve irritation of the bronchial tree.
The widespread use of measles vaccine, beginning in the late 1960s, raised
hopes for the eventual eradication of the disease; but, contrary to
expectations, the incidence of measles continued to rise worldwide. One of
the great problems with the measles vaccine is that it is a live vaccine
that rapidly becomes inert if exposed to warm temperatures; 10 minutes in
sunlight is sufficient to kill it. This sensitivity is a great hindrance
to its use in tropical areas. Research is currently directed toward
development of a more stable vaccine.
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Routine
Immunization
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WHO
schedule |
At Birth |
6 Weeks |
10 Weeks |
14 Weeks |
9 Months |
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BCG |
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OPV |
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DPT |
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HepB* |
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Hib |
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Measles with Vitamin A dose |
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Immunization may occur naturally, as when a person is exposed
unintentionally to a pathogen (any infectious agent), or it may be brought
about artificially through a vaccine. In either case, immunization provides
resistance, or immunity, to a particular pathogen by means of antibody
proteins that are targeted to eliminate that pathogen from the body. These
antibodies do not react to the entire pathogen but only to a specific part
of it, which is called an antigen. An individual can acquire immunity for a
specific pathogen passively or actively. In passive immunization a person
receives antibodies or lymphocytes that have been produced by another
individual's immune system; in active immunization the individual's own
immune system is stimulated to produce antibodies and lymphocytes.
Passive immunization imparts immediate, but not long-lasting, protection
against a pathogen and may arise naturally, such as when a fetus receives
antibodies from the mother across the placenta or when a breast-feeding
infant ingests antibodies in the mother's milk. Passive immunization against
a particular pathogen, such as the hepatitis B virus (HBV), also can be
conferred artificially. A person lacking immunity to HBV can receive a
preparation called immune serum globulin that contains antibodies formed
against the virus. These antibodies are obtained from serum taken from
animal or human donors who previously were infected by or immunized against
the virus.
Active immunization stimulates the immune system to produce antibodies
against a particular infectious agent. Active immunity can arise naturally,
as when someone is exposed to a pathogen. For example, an individual who
recovers from a first case of the measles is immune to further infection by
the measles-causing virus, because the virus stimulates the immune system to
produce antibodies that specifically recognize and neutralize the pathogen
the next time it is encountered. Active immunization also can be
artificially induced through vaccination. Vaccines are preparations
containing antigens that stimulate an immune response without causing
illness. The purpose of vaccination is to ensure that a large enough number
of antibodies and lymphocytes capable of reacting against a specific
pathogen or toxin are available before exposure to it occurs. Active
immunization is often long-lasting and may be reactivated quickly by a
recurrence of the infection or by revaccination.
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