Rosalee Brown
JUST A few days ago I received a call from a lady who told me she was pregnant and was concerned about her calcium consumption because she did not drink milk. I tried to assure her that she was worrying unduly, as there were many other excellent sources of calcium.
WHAT IS CALCIUM?
Calcium is one of the major minerals in the body; the others are magnesium, phosphorus, sodium, potassium and chloride. These minerals are present in the largest amounts and are needed in the greatest quantities. A different amount of dietary calcium is recommended at different stages of the life cycle and there are certain periods when the demand is great, for example during rapid growth periods, pregnancy and lactation.
The 1993 Dietary Recommendation for the Caribbean recommends 400mg of calcium for children zero to six months. The amounts increased with age, but the periods 15-18 years, pregnancy and lactation have the highest recommendation of 900mg and 1000mg respectively. The more recent Dietary Reference Intake (DRI) from the United States of America recommends 1300 mg for nine to 18 year olds and 1000 mg for 19-50 year olds, but 1200 mg for those older than 50.
The Tolerable Upper Limit, which is the maximum intake by an individual that is unlikely to pose a risk of adverse health effects and includes all dietary sources such as foods and supplements, is 2500mg of calcium in all age groups.
Calcium is needed for numerous functions in the body including building bones and teeth, blood clotting, the transmission of nerve impulses and the regulation of heart rhythm. Ninety-nine per cent of the body's calcium is found in bones and teeth and the remainder is found in blood and other tissues.
HEALTHY BONES
Bones are living tissues that are constantly breaking down and building up, a process called remodelling. The bone cell osteoblast, builds bones while the cell osteoclast breaks them down. In healthy persons who consume adequate dietary calcium and get adequate physical activity, bone production exceeds bone breakdown up to about age 30, after that, breakdown tends to exceed building. This fact is important because the period up to age 30 should be capitalised on for maximum bone storage.
Vitamin D is a very important nutrient in the absorption of calcium which, in Jamaica, we should get an adequate supply of with the assistance of sunshine. The loss of bone during ageing is due to factors such as genetics, physical inactivity and lower levels of circulating hormones (oestrogen in women and testosterone in men).
Since the period of pregnancy is one of the periods when the demand for calcium is greatest, adequate dietary intake is necessary for the development of the baby, to prevent pre-eclampsia (which is high blood pressure in the third trimester) and to protect the mother's skeleton from weakening.
Not all of the calcium consumed is absorbed - not even from dairy sources and some plant sources have fibre and phytate which can decrease absorption and retention. Some vegetables have oxalate which can bind calcium, reducing it's bioavailability. Other minerals such as magnesium, if in excess, can compete with calcium for absorption.
The very important rule of eating a variety of whole foods is always important and since calcium is available from many sources, including milk. Variety in the diet is strongly encouraged.
Rosalee Brown is a registered dietitian/nutritionist who operates Integrated Nutrition and Health Services; email: yourhealth@gleanerjm.com.
