Introduction to Human Nutrition

Minerals and Trace Elements 193

intake to BMD and BMC to establish the estimates of
calcium intake requirements for pregnancy and lacta-
tion. Desirable calcium retention, which is based on
balance data, may be considered a functional indica-
tor of nutritional adequacy of calcium in population
groups and was used by the US Food and Nutrition
Board in 1997 to establish recommendations for daily
calcium intakes. This is based on the concept that
to maximize skeletal strength, optimum bone mass
must be attained through a maximum skeletal calcium
reserve. Finally, recent research suggests that bio-
chemical markers of bone turnover that predict bone
mass changes and fracture risk may be functional
indicators of the adequacy of calcium intake. This
requires more investigation.

Requirements and dietary sources

Milk and milk products are the most important
dietary sources of calcium for most people in Western
countries, with cereal products and fruits and vegeta-
bles each making a much smaller contribution (Table
9.2). For example, the contribution of dairy products
to total calcium intake has been estimated as 73% in
the Netherlands, 51–52% in Germany, 51–52% in the
USA, 57% in the UK and 44% in Ireland. Tinned fi sh,
such as sardines, are rich sources of calcium but do
not make a signifi cant contribution to intake for most
people. In general, foods of plant origin are not very
rich sources of calcium. However, owing to the level
of consumption, foods of plant origin make a signifi -
cant contribution to total calcium intake. For example,
in the USA, cereals contribute about 25–27% of total
calcium intake, whereas in the UK cereals contribute
about 25% of total calcium intake with about 14%
from bread because of calcium fortifi cation of white
fl our. Increased availability of calcium-fortifi ed foods
and dietary supplements containing calcium salts is
leading to a wider range of rich dietary sources of
calcium. Contributions from nutritional supplements
or medicines may be signifi cant for some people.
Given the high proportion of body calcium which is
present in bone, and the importance of bone as the
major reservoir for calcium, development and main-
tenance of bone is the major determinant of calcium
needs. Thus, unlike other nutrients, the requirement
for calcium is considered to relate not to the mainte-
nance of the metabolic function of the nutrient but
to the maintenance of an optimal reserve and the
support of the reserve’s function (i.e., bone integrity).

Calcium requirements, therefore, vary throughout an

individual’s life, with greater needs during the periods

of rapid growth in childhood and adolescence, during

pregnancy and lactation, and in later life. There are

important genetic and environmental infl uences of

calcium requirements. Genetic infl uences include

such factors as bone architecture and geometry, and

responsiveness of bone to hormones that mediate the

function of bone as the body’s calcium reserve.

Environmental infl uences include factors such as

dietary constituents and the degree of mechanical

loading imposed on the skeleton in everyday life.

Because of their effects on urinary calcium losses,

high intakes of both sodium and protein increase

dietary calcium requirements.

There is considerable disagreement over human

calcium requirements, and this is refl ected in the wide

variation in estimates of daily calcium requirements

made by different expert authorities. For example,

expert committees in the USA and the EU have

Table 9.2 Calcium and phosphorus contents of some common foods

Range (mg/100 g)

Food source Description Ca P

Cheese Hard, from milk 400–1200 400–810

Cheese Soft, from milk 60–700 100–790

Sardines Tinned, in oil 550 520

Milk Cow’s (3.9, 1.6 and

0.1% fat)

115–120 92–94

Yoghurt Whole milk 160–200 130–170

Ice cream Dairy 110–130 99–110

Eggs Chicken, raw, whole 57 200

Chicken,

duck,

turkey

Raw 9–12 190–200

Beef, mutton,

pork

Raw 7–10 60–200

Cod, plaice,

whiting

Raw 16–51 170–180

Wheat fl our Whole fl our 38 320

Wheat fl our White fl our 15–140 110–120

Bread White 100–180 79–120

Bread Brown 100–140 150–180

Spinach Raw 170 45

Watercress Raw 170 52

Broccoli Green, raw 56 87

Peas Processed, canned 33 89

Rice Raw, white, polished 18–25 54–67

Potatoes Raw 5–6 34–37

Tofu Soyabean, steamed, or

fried

510–1480 95–270

Data from Holland et al. (1995). Reproduced with permission from

HMSO.