Vitamin C (ascorbic acid)
Vitamin C has antioxidant properties, potentially protecting cells from oxidative damage caused by free radicals. Vitamin C is also involved in the synthesis of collagen which is required for the normal structure and function of connective tissues such as skin, cartilage and bones. It is therefore an important nutrient for the healing process. It is also involved in the normal structure and function of blood vessels and neurological function. Vitamin C also increases the absorption of non-haem iron (iron from plant sources) in the gut.
Severe deficiency of vitamin C leads to scurvy. Signs of deficiency do not manifest until previously adequately nourished individuals have been deprived of vitamin C for 4-6 months. Deficiency is associated with fatigue, weakness, aching joints and muscles. Most of the other symptoms of scurvy are due to impaired collagen synthesis and are characterized by bleeding gums, poor wound healing and damage to bone and other tissues.
Acute high doses of vitamin C are occasionally associated with diarrhoea and intestinal discomfort. A significant number of people take high dose (1000mg) vitamin C supplements (the RNI for adults is 40mg/day); however there is no evidence that this either confers any benefit or presents negative health consequences.
Fresh fruits especially citrus fruits and berries; green vegetables, peppers and tomatoes are all sources of vitamin C. It is also found in potatoes (especially new potatoes).
The bioavailability and absorption of vitamins
The bioavailability of a vitamin (i.e. how readily it can be absorbed and used by the body) may be influenced by a variety of factors. The proportion of a vitamin absorbed from the diet following consumption can vary, and will depend upon the individual person’s needs, their ability to absorb nutrients, the amount available to them and other components of the diet. For example, vitamin C can enhance the absorption of non-haem iron when foods or drink containing both vitamin C and non-haem iron are consumed in the same meal. Some vitamins, e.g. vitamin C and riboflavin, are labile and susceptible to damage by heat, light, oxygen, enzymes and minerals and these losses may occur during food processing, preparation and storage.
The bioavailability of vitamins is discussed in detail by the FSA Expert Group on Vitamins and Minerals (http://www.food.gov.uk/multimedia/webpage/vitandmin/).
Although most people are able to meet their requirements for vitamins by eating a varied diet, there are certain groups of the population who have higher than normal requirements for some nutrients, e.g. ill people, those taking certain drugs and pregnant women. Such people need to ensure they eat foods rich in particular vitamins and sometimes supplements are advised. Infants and young children are recommended to have supplements of vitamins A, C and D up to age 5 years. Vitamin D supplements are also recommended for older people and pregnant and lactating women. Some women may require additional iron if menstrual losses are high and folic acid is advised for women planning a pregnancy and for pregnant women in the first 12 weeks of pregnancy.
A UK survey of adults undertaken in 2000/2001 found that 40% of women and 29% of men were taking dietary supplements compared with 17% and 9% respectively in 1986/1987. The use of vitamin and mineral supplements in the UK was assessed by the Expert Vitamin and Mineral Committee in 2000. This group also set upper limits for vitamins and minerals (http://www.food.gov.uk/science/ouradvisors/vitandmin/).
Page created July 2009. Revised February 2016.