Nutrition, Vitamins and Diseases

Food is not just something that fills the stomach. It supplies the energy that keeps us alive, the raw material to build and repair the body, and the protective substances that prevent disease. The six classes of nutrients are carbohydrates, proteins, fats, vitamins, minerals and water (dietary fibre is also counted as a seventh helper). The first three are needed in large amounts and are called macronutrients; vitamins and minerals are needed in tiny amounts and are called micronutrients.

Why do fats give more than twice the energy of carbohydrates? A fat molecule has far more carbon-hydrogen bonds and much less oxygen, so more of it can be 'burnt'. That is why the body stores spare energy as fat, and why 1 g of fat gives about 9 kcal against about 4 kcal for 1 g of carbohydrate or protein.

Proteins are long chains of amino acids. Our bodies need 20 amino acids; of these, 9 are essential amino acids that the body cannot make and must take from food (the rest are non-essential). Proteins of animal origin (milk, egg, meat, fish) contain all the essential amino acids and are called complete proteins. Most plant proteins miss one or two, so a mix such as dal with rice or roti makes a complete protein. Among plants, the soyabean is the richest source of protein.

A balanced diet contains all nutrients in the right proportion for a person's age, sex, body size and work, with enough water and fibre. A growing child, a pregnant woman, an athlete and an office worker need different amounts. Radhika's school tiffin of roti, dal, a vegetable, curd and a fruit is a fine example: it has energy foods, body-building foods and protective foods together. Malnutrition means a poor diet in any direction, too little or too much, and includes both undernutrition and obesity.

ORS (oral rehydration solution) saves lives in diarrhoea and cholera. Diarrhoea drains water and salts (sodium, potassium) from the body, and the person can die of dehydration. ORS gives water, salts and a little glucose; the glucose helps the gut absorb sodium and water together. In India, Dr Dilip Mahalanabis was a pioneer in using ORS, during the 1971 refugee crisis. Home-made ORS is a pinch of salt and a spoon of sugar in a glass of clean water.

Vitamins are organic compounds that the body needs in tiny amounts to run its chemical reactions smoothly, but cannot make in sufficient quantity (a few exceptions exist, noted below). They do not give energy; they act as helpers and protectors. The word 'vitamine' was coined by Casimir Funk in 1912. A shortage causes a deficiency disease; too much of the fat-soluble ones causes hypervitaminosis.

Vitamin D is a vitamin and a hormone at the same time. When UV-B rays of sunlight fall on the skin, a skin chemical (7-dehydrocholesterol) is turned into Vitamin D, so a few minutes of morning sun is a real source. That is why Vitamin D is called the 'sunshine vitamin'.

Minerals are inorganic elements, such as calcium, iron and iodine, that the body needs for building bones, making blood, running nerves and controlling chemical reactions. Plants take them from the soil, and we get them from plants and animals. Those needed in larger amounts (more than about 100 mg a day) are macrominerals: calcium, phosphorus, sodium, potassium, magnesium, chlorine and sulphur. Those needed in tiny amounts are trace minerals: iron, iodine, zinc, copper, fluorine, selenium, cobalt and manganese.

Why iodine and goitre? The thyroid gland makes thyroxine, and a thyroxine molecule contains iodine. If the diet lacks iodine, the thyroid cannot make thyroxine; the pituitary keeps sending TSH to ask for more, and under that constant stimulation the gland swells. This swelling in the neck is goitre. It is common in hilly areas, because iodine is washed out of the soil. The cure is cheap: iodised salt.

For this reason table salt is fortified with iodine (as potassium iodide or potassium iodate), a small amount that is safe and does not change the taste. Fortification means adding a missing nutrient to a common food so that a whole population gets it. Other examples are iron-fortified flour and Vitamin D-fortified milk.

A disease is any state in which the body does not work normally. Communicable (infectious) diseases are caused by living agents called pathogens and can spread from one person to another; non-communicable diseases (diabetes, cancer, heart disease) cannot. The father of the germ theory of disease is Louis Pasteur, and Robert Koch proved that a particular germ causes a particular disease (anthrax, 1876). Koch also discovered the bacilli of tuberculosis (1882) and cholera (1883).

Word check: an endemic disease stays constantly in one region (goitre in hills, kala-azar in parts of Bihar); an epidemic is a sudden rise of cases in a region; a pandemic spreads worldwide (COVID-19); a sporadic disease occurs in scattered, irregular cases. A carrier harbours the germ without symptoms but can spread it (Typhoid Mary).

AIDS stands for Acquired Immuno-Deficiency Syndrome. It is caused by the Human Immunodeficiency Virus (HIV), a retrovirus whose genetic material is RNA. Think of the immune system as an army. HIV does not attack the body directly; it kills the army's commanders, the helper T-lymphocytes (CD4 cells). Slowly the body loses the power to fight even ordinary germs, and the person dies not of HIV itself but of infections and cancers that a healthy person would resist (opportunistic infections). AIDS was first recognised in 1981, and the virus was isolated in 1983 by Luc Montagnier and Françoise Barré-Sinoussi (Nobel Prize, 2008).

Sexually transmitted infections (STIs), also called STDs or venereal diseases, spread mainly through sexual contact. They can be caused by bacteria, viruses or protozoa, so the same list can be asked in different ways. Bacterial STIs: syphilis (Treponema pallidum), gonorrhoea (Neisseria gonorrhoeae), chlamydia. Viral STIs: HIV/AIDS, genital herpes (HSV-2), genital warts and cervical cancer (HPV), and hepatitis B. Protozoan STI: trichomoniasis (Trichomonas vaginalis). Bacterial STIs can be cured with antibiotics if treated early; viral ones can be controlled but not fully cured (except that HPV and hepatitis B have vaccines).

Prevention is the real cure. The surest protection is a single, faithful partner. Use condoms (a barrier method that also gives contraception and protects against STIs such as AIDS and gonorrhoea), use only fresh, disposable needles and syringes, accept only screened blood, and get an infected pregnant woman treated with ART to protect her baby. Early testing and treatment, along with support instead of stigma, are part of the control programme.

Immunity is the body's power to resist disease-causing organisms (pathogens). It works at two levels. Innate (natural) immunity is present from birth and is non-specific: skin, mucus, stomach acid, tears and saliva (lysozyme), and cells such as phagocytes (neutrophils, macrophages) that swallow germs. Acquired immunity is developed during life, is specific to one pathogen and has memory, so a second attack is met faster and harder. It is built by lymphocytes: B-cells make antibodies (humoral response) and T-cells attack infected cells directly (cell-mediated response).

An antigen is any foreign substance (a protein or a part of a germ) that triggers an immune response by binding to receptors on lymphocytes. An antibody (immunoglobulin) is the protein the body makes against it. Five classes exist: IgG (most abundant, about 75% of blood antibodies, crosses the placenta), IgA (in saliva, tears, milk and gut secretions), IgM (the first to appear in an infection, the largest), IgE (allergy and worm infections) and IgD (on the surface of B-cells).

A vaccine teaches the body about a germ without causing the disease. It gives an active artificial immunity and leaves memory cells. Types: live attenuated (weakened germ: BCG, oral polio or Sabin, measles, MMR); inactivated or killed (Salk polio, rabies, hepatitis A); toxoid (inactivated toxin: tetanus, diphtheria); subunit or recombinant (a protein only: hepatitis B, HPV); mRNA (instructions to make a viral protein: some COVID-19 vaccines); viral vector (a harmless virus carries the antigen gene: some COVID-19 vaccines). The principle was first shown by Edward Jenner in 1796, who used cowpox material against smallpox.

India's immunisation programmes. The Universal Immunisation Programme (UIP) provides free vaccines to children and pregnant women against a set of diseases that includes TB, diphtheria, pertussis (whooping cough), tetanus, polio, measles, hepatitis B and others. Mission Indradhanush, launched in 2014, aims to reach children and pregnant women who are partially or fully unvaccinated. The Pulse Polio campaign began in 1995 and India was certified polio-free by the WHO in 2014. Antibiotics (penicillin, streptomycin, tetracycline) kill or stop bacteria; they do not work on viruses and should not be used as a preventive 'hygiene' measure, because overuse causes antimicrobial resistance.

Diabetes mellitus is a disorder in which blood glucose stays high because the pancreas does not make enough insulin (made by the beta cells of the islets of Langerhans) or the body cells stop responding to it. Classic symptoms are passing a lot of urine, excessive thirst and hunger, and weight loss. Insulin was isolated by Frederick Banting and Charles Best in 1921-22 at Toronto; Banting and Macleod shared the 1923 Nobel Prize. Insulin lowers blood sugar, while glucagon (alpha cells) raises it. Today human insulin is made by recombinant DNA technology in bacteria (Humulin, the first genetically engineered human insulin, 1982). World Diabetes Day is on 14 November, Banting's birthday.

Hypertension (high blood pressure) is a sustained pressure of about 140/90 mm Hg or more, whereas the normal value is about 120/80. It strains the heart and harms the brain, kidneys and eyes. Obesity is excess body fat; it is judged by BMI = weight (kg) divided by height (m) squared: below 18.5 underweight, 18.5 to 24.9 normal, 25 to 29.9 overweight, 30 and above obese (WHO). Together with a high-fat diet, smoking and stress, these cause lifestyle diseases such as heart disease, stroke and type 2 diabetes. India's National Programme for Prevention and Control of NCDs (launched in 2010 for cancer, diabetes, cardiovascular disease and stroke) targets them.

Cancer is uncontrolled cell division. Normal cells stop dividing when they touch neighbours (contact inhibition); cancer cells lose this. A benign tumour stays in one place; a malignant tumour invades nearby tissue and spreads through blood and lymph to other organs, which is called metastasis. Types: carcinoma (epithelial tissue, the commonest), sarcoma (bone, muscle, connective tissue), leukaemia (white blood cells, blood cancer) and lymphoma (lymph nodes). Carcinogens include tobacco smoke (lung and mouth cancer), UV rays (skin cancer), X-rays and gamma rays, asbestos, benzene, aflatoxin (liver) and viruses such as HPV (cervix). Detection: biopsy, X-ray, CT, MRI, mammography. Treatment: surgery, radiotherapy, chemotherapy and immunotherapy (for example alpha-interferon). World Cancer Day is on 4 February.

Drug abuse is the use of drugs for non-medical purposes, in amounts that harm the body and mind, and it leads to addiction and dependence. Opioids (morphine, heroin) come from the opium poppy Papaver somniferum; heroin is chemically diacetylmorphine, made from morphine. Cannabinoids (marijuana or bhang, ganja, charas) come from Cannabis sativa. Cocaine comes from the coca plant Erythroxylum coca. Nicotine (tobacco) and alcohol are also addictive. Warning signs include a drop in studies, withdrawal from friends, mood swings and secrecy. Help comes from counselling, medical treatment and family support. The International Day against Drug Abuse is 26 June.

The same chemical can be both: phenol 0.2% is an antiseptic, phenol 1% is a disinfectant. The difference is concentration and where it is used (living tissue versus non-living objects).