Calcium is a major mineral essential for healthy bones and teeth. There are several minerals known to be essential to the human body and which must be obtained from food. The major minerals (calcium, magnesium, phosphorus, sodium, chloride and potassium) are needed in the greatest quantities or are present in large amounts in the body. The three main functions of minerals are as constituents of the skeleton, as soluble salts which help control the composition of the body fluids, and as essential adjuncts to the action of many enzymes and other proteins.
Calcium Requirements
The UK Department of Health recommended Reference Nutrient Intake (RNI) for calcium is as follows. The RNI is a daily amount that is enough or more than enough for 97% of people. The RNI is similar to the Recommended Daily Amount used previously in the UK.
Age/Sex Calcium requirement (mg/day)
Infants & children, depending on age 350-550
Teenage girls 800
Teenage boys 1000
Adult men & women 700
Breast-feeding women extra 550
The 1989 US recommendations are generally slightly higher. In 1994 the US recommendations for children aged 1-10 was increased from 800mg to 1,200mg daily and for young adults aged 11-24 years it was increased from 1,200 to 1,500mg. During pregnancy and breast feeding women in the USA are now advised to have 1,400mg calcium daily and American men and women over the age of 50 years are advised to increased their calcium intake towards 1,500mg because the intestinal absorption of calcium declines with age.
Vegan Sources of Calcium
Good plant sources of calcium include tofu (if prepared using calcium sulphate contains more than four times the calcium of whole cow's milk), green leafy vegetables, seeds and nuts. The calcium in green vegetables which are not high in oxalate e.g. kale, is absorbed as well or better than the calcium from cow's milk. Some soya milks e.g. Provamel, Plamil, Granovita are fortified with calcium. Drinking hard water can provide 200mg of calcium daily but soft water contains almost none. Other calcium rich foods include black molasses, edible seaweeds, watercress, parsley and dried figs.
Examples of amounts of foods providing 100mg calcium
Black molasses 20g
Dried figs 40g
Almonds 42g
Soya flour 44g
Parsley 50g
Kale 67g
Brazils Nuts 59g
Wholemeal bread 185g
Protein & Calcium
A high protein diet, especially derived from animal foods, causes calcium loss in the body. The higher sulphur-to-calcium ratio of meat increases calcium excretion, and a diet rich in meat can cause bone demineralisation. A report published in 1988 comparing the amounts of calcium excreted in the urine of 15 subjects showed that the animal-protein diet caused greater loss of bone calcium in the urine (150mg/day) than the all-vegetable protein diet (103mg/day). These findings suggest that diets providing vegetable rather than animal protein may actually protect against bone loss and hence osteoporosis. In one study adults on a low-protein diet were in calcium balance regardless of whether calcium intake was 500mg, 800mg or 1400mg a day. Interestingly The American Dietetic Association, in its 1993 policy statement on vegetable diets, pointed out that the calcium intakes recommended in the USA were increased specifically to offset calcium losses caused by the typically high protein consumption in that country.
Calcium Absorption
Only 20-30% of calcium in the average diet is absorbed. Calcium absorption can be reduced because it binds to fibre, phytate or oxalate in the intestine. Vegan diets contain more than average of these substances. Fibre is no longer thought to limit the availability of calcium from food. Phytate or phytic acid is found in grains, nuts and seeds and can bind with calcium making it less absorbable. However, the body does adapt to lower levels of available calcium and the American Dietetic Association and the UK's Ministry of Agriculture, Fisheries & Foods as well as the Department of Health believe that fibre, phytate and oxalate do not have a significant effect on calcium intake overall.
Although the calcium intake of adult vegans tends to be lower than the recommended optimum, it is close to the Estimated Average Requirement. There have been no reports of calcium deficiency in adult vegans.
The Estimated Average Requirement (UK) of a nutrient in the diet is an estimate of the average needs of a group of people. About half may need more, and half may need less.
Osteoporosis
Osteoporosis is the major cause of bone fractures in the elderly. One in four British women are affected by this disease. It is better prevented than treated and prevention includes an adequate intake of calcium throughout life, but especially in childhood and young adulthood; and minimising major risk factors e.g. smoking, heavy alcohol use and lack of physical exercise. Diets high in protein and in salt (sodium chloride) also increase calcium loss from the body and may have an effect on osteoporosis. Post-menopausal women are more prone to osteoporosis because they produce less oestrogen, which protects the skeleton in younger women.
There has been much publicity about the role of dietary calcium in preventing osteoporosis but the fact remains that it is more common in Westernised countries where calcium intakes and consumption of dairy products are high compared to the rest of the world.Osteoporosis is comparatively rare in rural subsistence cultures, even though calcium intakes are much lower. Lifestyle factors, such as physical activity, lower protein intakes, little alcohol consumption and the rarity of smoking, may offer protection to people in these populations.
