Vitamin A

Q My nine-year-old daughter is just recovering from a bad bout of measles. With this, she had an ear infection and conjunctivitis, and this is clearing up, but her cough seems to be lingering. I’m worried that her weakened immune system may not be able to fight the bugs that are flying around in school, especially during this time of the year.

Is there anything I can do to rapidly strengthen her immune system and increase her resistance to other infections? – WC, Surbiton

A Making sure your daughter replenishes her depleted levels of nutrients is definitely a step in the right direction. Vitamin A is a great infection-fighter but, sadly, it hasn’t enjoyed the same amount of media attention as its sexier cousins, vitamins C and E. Despite its crucial role in maintaining the smooth functioning of numerous bodily processes, the importance of vitamin A has been woefully underplayed.

Over 300 genes are regulated by the rapid action of vitamin A (Curr Issues Public Health, 1996; 2: 161-4). It is vital for healthy eyesight, bone growth, reproduction and embryonic development (Annu Rev Nutr, 2002; 22: 347-81; Birth Defects Res C Embryo Today, 2003; 69: 156-73; Lancet, 1994; 343: 87-8).

More important, vitamin A is essential for a healthy immune system. It maintains the surface tissues that line the eyes as well as the respiratory, urinary and intestinal tracts. These internal cellular linings (along with the skin) act as physical barriers to invasion by disease-causing bacteria and viruses. So, vitamin A helps the body resist infection by bolstering these mechanical defences.

In addition, this vitamin helps to regulate the immune system by enabling lymphocytes – the white blood cells that fight infection and disease – to do their jobs more effectively. HIV (human immunodeficiency virus)-positive patients are advised to fortify their diets with vitamin A-rich foods, and HIV-infected pregnant women who are deficient in this micronutrient have a three to four times greater risk of transmitting the HIV to their baby than is usual for this group (AIDS Action, 1995; 30 [Sep-Nov]: 4-5).

Indeed, there is a wealth of evidence highlighting the antiviral properties of vitamin A not just for battling against the common cold or flu, but also as tools for treating and preventing other infectious diseases, including measles.

WDDTY panellist Dr Patrick Kingsley is a strong advocate of vitamin A and its healing properties. To treat measles in young patients, he suggests giving them a shot of high-dose (20,000- 30,000 IU) vitamin A in the acute phase for some two or three days. Following this, the dosage can be reduced to 10,000 IU for about a week. After that, 5000 IU should be quite sufficient to see them back to recovery, says Dr Kingsley. The only thing to check for, he adds, is that they’re not getting headaches from the high dosages of vitamin A during the acute phase.

As your daughter is already in the recovery stage, this may be a good time for you to help her kick-start her immune system by giving her one cod-liver-oil capsule every day. According to Dr Kingsley, “Cod liver oil is one of the best ways to get a reasonable dose of not just vitamin A, but also vitamin D. Each capsule should typically contain around 4000 IU of vitamin A and 400 IU of vitamin D – this should help her get back to shape.”

Once she’s completely recovered, you could then cut back the dosage schedule to one capsule a week to maintain her immune system function.

One randomised, double-blind trial carried out in South Africa investigated the effectiveness of vitamin A in treating young children who had measles complicated by pneumonia, diarrhoea or croup (a disease of infants and young children characterised by harsh coughing, hoarseness, fever and breathing difficulties). The researchers found that the children who received vitamin A supplements recovered more quickly from the pneumonia and diarrhoea, and had fewer symptoms of the croup than those taking a placebo. Of the 12 children who died, 10 were taking a placebo (N Engl J Med, 1990; 323: 160-4).

Another study involving young children looked at vitamin A as a potential weapon against malaria. Scientists at the Johns Hopkins Hospital in Baltimore, Maryland, gave children living in areas of malaria epidemics in Papua New Guinea either high doses of vitamin A or a placebo, every three months for more than a year. The results showed that the vitamin-A group had 30 per cent fewer cases of malaria than the placebo (control) group, leading the study’s researchers to conclude that the vitamin could help children boost their immunity after exposure to the malaria-inducing pathogen Plasmodium falciparum (Lancet, 1999; 354: 203-9).

Animal studies have demonstrated the role of vitamin-A deficiency in increasing susceptibility to more serious diseases such as cholera and Staphylococcus aureus-induced arthritis (Infect Immun, 1993; 61: 3952-7; Infect Immun, 1996; 64: 209-14).

The benefits of vitamin A also stretch to cancer prevention. Studies investigating nutrition and cancer have almost invariably demonstrated a relationship between a deficiency of the vitamin and development of the disease. It has been suggested that the role of vitamin A in regulating cell division, cell differentiation and cell death works not only to prevent the proliferation and spread of abnormal, cancerous cells, but also by ‘apoptosis’ – medicalese for ‘programmed cell destruction’ (Expert Rev Mol Med, 2004; 6: 1-23).

ATRA (all-trans retinoic acid) is a metabolic form of vitamin A that has built itself quite a solid reputation in helping to treat acute promyelocytic leukaemia (APL) (Blood, 2004; 104: 3490-3; Zhonghua Zhong Liu Za Zhi, 1993; 15: 125-9). Recently, a ‘drug’ known as Lipo-ATRA (essentially ATRA wrapped in fat) has been licensed for use in this form of leukaemia after scientists found that it successfully reversed the condition in 74 of 84 patients (88 per cent) – without a need for chemotherapy.

In addition, there is a raft of studies that highlights the efficacy of vitamin A in hindering or reversing the development of cancer in a wide variety of tissues, such as from the breast, ovaries, cervix, mouth, colon and lungs (Anticancer Res, 2004; 24: 807-9; 1779-83; J Exp Clin Cancer Res, 2004; 23: 309-16; Cell Mol Life Sci, 2004; 61: 1475-84; Med Oral, 2001; 6: 114-23; J Nutr, 1993; 123: 634-41).

Meat, oily fish, cheese, whole milk and eggs are among the best sources of retinol, the active form of vitamin A, which can be metabolised to retinal (used by the eyes) and retinoic acid. Liver is a particularly rich source of this nutrient as it is where this vitamin is stored in animals as well as in humans.

Vitamin A is not found in plants, but certain fruits and vegetables do contain yellow/orange pigments called ‘carotenoids’. These compounds are converted to vitamin A by the liver when its store of retinol is depleted. Beta-carotene is one such carotenoid, and is found in a wide array of foods, including carrots, mangoes, sweet potatoes, spinach, cantaloupe melons, broccoli, oatmeal, tomatoes, papayas, oranges and carrots. In addition to serving as a vitamin A ‘stand-by’ for when the liver needs it, beta-carotene also acts as an antioxidant to protect cells from damage by harmful free radicals.

However, as with many things in life, you can have too much of a good thing. Too high a dose of vitamin A can be toxic and lead to a condition known as ‘hypervitaminosis A’. Symptoms of such vitamin A toxicity include headache, dizziness, blurred vision, joint pain, dry lips, scaly skin and hair loss. Most cases of hypervitaminosis A are due to an excess intake of vitamin-A supplements rather than from overconsumption of vitamin A-rich foods, although toxic symptoms can arise from consuming huge amounts of liver.

Too much beta-carotene can turn the skin yellow (not to be mistaken for jaundice, which turns the whites of the eyes yellow). However, this state is not considered dangerous to your health, and is easily reversible.

To maximise the metabolism and uptake of vitamin A, make sure your daughter’s diet also has an adequate intake of zinc, protein and calories. These are needed to make retinal-binding protein, essential for the release of vitamin A from the liver and into the general circulation. An iron deficiency also limits the body’s utilisation of vitamin A.