INTRODUCTIONINTRODUCTION• During gestation the average foetus

requires about 30 g of calcium to mineralize its skeleton and maintain normal physiological processes.

• The suckling neonate requires more than this amount in breast milk during six months of exclusive lactation

• Although pregnant and lactating women face a comparable demand in the amount of calcium

• During pregnancy and lactation, 200–300 mg Ca/d is either transferred via the placenta to the foetus or excreted in breast

milk.

• The provision of calcium during pregnancy and lactation requires– Physiologic adaptation of calcium homeostatic

mechanisms.

– Including1. intestinal calcium absorption

2. urinary calcium excretion

3. maternal bone calcium turnover

TABLESelected examples of recommended dietary allowances for calcium in different countries

Women Pregnancy Lactation

mg/d mg/d mg/dAustralia-1989 800 1100(+300) 1200(+400)

FAO/WHO 1974+

450 1100(+650) 1100(+650)

France 1988 800 1000(+200) 1200(+400)Indonesia 1980 500 600(+100) 600(+100)

Ireland 1984 800 1200(+400) 1200(+400)Spain 1983+ 600 1325(+725) 1425(+825)United Kingdom1991

700 700(0) 1250(+550)

United States 1989

800 1200(+400) 1200(+400)

• Calcium stress of pregnancy is relatively similar among women

• The amount of calcium secreted during lactation can be highly variable, depending on

1. Amount of breast-milk produced

2. Breast-milk calcium concentration

3. Length of the lactation period

Calcium

• Calcium is important for a number of functions in the body

• It is essential for

1. Growth

2. Maintenance of bones and teeth

3. Nerve transmission

4. Muscle contraction

5. Number of other cell processes

• The body has increased calcium needs during growth spurts, pregnancy and lactation

• An inadequate calcium intake can therefore cause a number of problems

• In growing children and adolescents, this can lead to stunted growth, and a reduced peak bone density increasing the risk of osteoporosis later in life

• In pregnancy, the unborn child will draw on the mother’s calcium stores to meet its needs, putting the condition of the mother’s bones and teeth at risk

Recommended Daily Intake

Population Group RDI

Adults 800 mg/day

Pregnancy 1100 mg/day

Lactation 1300 mg/day

Elderly 1000 mg/day

Sources of calciumFood Serving size Calcium (mg)Full cream Milk 250 ml (1 glass) 285

Natural Yoghurt 200g (1 tub) 340

Cheddar cheese 2 slices (40g) 310

Cooked Spinach 1 cup (100g) 170

Cooked broccoli 1 cup (100g) 30

Canned salmon (plus bones)

100g 230

Canned salmon (plus bones)

3 sardines (50g) 190

Almonds 45g 50

Availability in the diet

• Reduce calcium’s availability and absorption in the gut:

1. Fibre – soluble pectin fibre binds with the calcium

2. Fat – forms a soap in the stomach when it binds with calcium

3. Phytic acid – found in breakfast cereals

4. Oxalic acid – found in high concentrations in spinach and rhubarb, and in smaller amounts in sweet potatoes and dried beans.

Including calcium in the diet

• It’s easy to include dairy foods in a healthy, balanced diet. Have a look at these simple ideas:

– Have some milk with your breakfast cereal

–Wake up to a home-made banana, mango or strawberry smoothie

– Try some cheese on toast

– Nothing beats cream cheese on a bagel

–Try yoghurt at morning tea to keep you going until lunch

–Sprinkle some cheese on your potato

–Have some fresh fruit and yoghurt for dessert

–Enjoy a warm cup of milk before bed

If dairy foods are not consumed there are many other ways to incorporate calcium into your diet:

–Try some calcium-enriched soymilk with muesli

–Have tuna and tomato on toast for breakfast

– Use calcium-fortified bread to make a sandwich

–Snack on a handful of nuts

–Have a stirfry of Asian green vegies

Pregnancy

• The normal foetal skeleton has accreted about 30 g calcium by the end of gestation

• About 80% of the accretion occurs rapidly during the third trimester

• Daily accretion rate of about 250–300 mg calcium by the foetal skeleton during the third trimester

The mother could theoretically meet this demand by

Increasing the intestinal absorption

Decreasing renal calcium losses

Increasing the resorption of calcium from the maternal skeleton

Minerals and hormones

• Earliest apparent changes in calcium balance in pregnancy is a fall in total serum calcium

• Serum calcitonin levels are increased during pregnancy

• PTHrP levels have been increased during pregnancy

• Other hormones are clearly in flux during pregnancy

Intestinal calcium absorption

• Intestinal absorption of calcium is doubled during pregnancy

• The increase in intestinal calcium absorption is associated with

– Doubling of 1,25-dihydroxyvitamin D levels

– Increased intestinal expression of the vitamin D-dependent calcium-binding protein calbindin-D

Renal calcium excretion• The 24-h urine calcium excretion is

typically increased as early as the 12th week of gestation

• This increase is likely a consequence of

– Increased intestinal absorption of calcium

– Increased renal filtered load of calcium

– Increased glomerular filtration rate

• In the fasted state, the calcium excretion is normal or even low.

Osteoporosis in pregnancy

• Occasionally, a woman will suffer an apparent fragility fracture during

pregnancy or in the first few weeks after delivery

• low bone mineral density reading will be obtained

• Focal, transient osteoporosis of the hip is a rare

Lactation

• The typical daily loss of calcium in breast milk has been estimated to range from 280–400 mg

• Although daily losses as great as 1000 mg

• A temporary demineralization of the skeleton seems to be the main mechanism

Again, the mother could theoretically meet this demand by

• increasing the intestinal absorption of

calcium

• decreasing renal calcium losses

• increasing the resorption of calcium from the maternal skeleton

Minerals and hormones

• The mean ionized calcium level of exclusively lactating women is increased, although it remains in the normal range

• Serum phosphate levels are also increased and may exceed the normal range

• Intact PTH, as determined by a two-site IRMA, has been found to be reduced 50% or more in lactating women in the first several months postpartum

Intestinal calcium absorption

• The intestinal absorption of calcium is equal to the no pregnant state

–Decreased from pregnancy

• This change coincides with the fall in 1,25-dihydroxyvitamin D levels to normal.

Renal calcium excretion

• The GFR falls during lactation to a level below the pregnant and pre pregnant value

• Tubular reabsorption of calcium must be increased

• Renal excretion of calcium is typically

reduced to levels as low as 50 mg/24 h

• increased serum calcium

• Acute estrogen deficiency (e.g. GnRH analog therapy)

→increases skeletal resorption and

→raises the blood calcium;

→in turn, PTH is suppressed and

→renal calcium losses are increased.

• During lactation, the combined effects of PTHrP (secreted by the breast) and estrogen deficiency

→increase skeletal resorption

→reduce renal calcium losses, and

→raise the blood calcium,

→but calcium is directed into breast milk.

  

Acute estrogen deficiency (e.g. GnRH analog therapy) increases skeletal resorption and raises the blood calcium; in turn, PTH is suppressed and renal calcium losses are increased. During lactation, the combined effects of PTHrP (secreted by the breast) and estrogen deficiency increase skeletal resorption, reduce renal calcium losses, and raise the blood calcium, but calcium is directed into breast milk.

Osteoporosis of lactation

• Like osteoporosis in pregnancy

• Woman may have had low bone density before conception

• PTHrP levels were high in one case of lactational osteoporosis

CALCIUM PHYSIOLOGY DURING PREGNANCY

• Calcium provided from the maternal deciduas aids in fertilization of the egg and implantation of the blastocyst

• About 80% of the calcium present in the foetal skeleton at the end of gestation crossed the placenta during the third trimester

• Intestinal calcium absorption doubles during pregnancy

Bone mobilization

• Investigated changes in bone mineral content during pregnancy and lactation

• Bone loss at certain skeletal sites, such as the lumbar spine and femoral neck

Mineral Ions

• Several characteristic changes in maternal serum chemistries and calciotropic hormones during pregnancy

• Serum albumin and hemoglobin fall during pregnancy due to hemodilution

• Serum phosphate and magnesium levels remain normal during pregnancy.

Schematic illustration of the longitudinal changes in calcium during pregnancy and

lactation.

Schematic illustration of the longitudinal changes in phosphate PTH during pregnancy

and lactation.

Schematic illustration of the longitudinal changes in 25-hydroxyvitamin D or calcifediol (25-D), Calcitonin

during pregnancy and lactation.

Schematic illustration of the longitudinal changes in calcium during pregnancy and

lactation.

Parathyroid Hormone

• Parathyroid hormone (PTH) was first measured with assays that reported high circulating levels during pregnancy

• Those early-generation PTH assays measured many biologically inactive fragments of PTH

• In contrast, in women from Asia and Gambia who have very low dietary calcium intakes

Vitamin D Metabolites

• A common concern is that the placenta and fetus will deplete maternal 25-D stores, but this does not appear to be the case

• Even in severely vitamin D deficient women there was either no change or at most a nonsignificant decline in maternal 25-D levels during pregnancy.

Calcitonin

• Serum calcitonin levels are increased during pregnancy and may derive from–Maternal Thyroid

– Breast

– Decidua

– Placenta

• Calcitonin plays an important role in the physiological responses to the calcium demands of pregnancy

PTHrP

• PTHrP levels are increased during the third trimester

– but whether this occurs earlier in pregnancy

• PTHrP is produced by many tissues in the fetus and mother and it is unknown which source(s) account for the rise in PTHrP 1-86 detected in the maternal circulation

Other Hormones

• Calciotropic hormones

–Response to challenges such as hypocalcemia

• Steroids

• Prolactin

• Placental lactogen

• IGF-1

Renal Handling of Calcium

• Renal calcium excretion is increased as early as the 12th week of gestation and 24 hour urine values (corrected for creatinine excretion) can exceed the normal range.

• Conversely, fasting urine calcium values are normal or low, confirming that the hypercalciuria is a consequence of the enhanced intestinal calcium absorption.

Consequences of bone loss during pregnancy and Lactation

• Maternal bone loss during pregnancy or lactation might lead to osteoporosis and fracture either contemporaneously or, by reducing peak bone mass, in later life.

• Severe bone loss leading to osteoporosis and fracture is a well recognized but rare complication of pregnancy and lactation

Influence of calcium intakes on breast-milk calcium secretion

• Breast-milk calcium secretion is known to be independent of recent maternal calcium intake

• No relationships between breast-milk calcium concentrations and maternal calcium intakes

• However, there have been no definitive investigations in women with low calcium intakes.

Effect of maternal calcium intake on foetal and infant growth

• Marginal calcium deficiency may be associated with reduced bone mineral content

• The influence of maternal calcium intakes during pregnancy and lactation on the growth and bone development of the foetus and breast-fed baby is not known

Calcium intakes and hypertensive disorders of pregnancy

• A potential connection between low calcium intakes and hypertensive disorders in pregnancy was suggested by the fact that the incidence of eclampsia is highest in countries where calcium intakes are low.

• Several well-conducted trials have studied the efficacy of calcium supplements in preventing preeclampsia, gestational hypertension, and premature delivery, as summarized in Table

Biochemical changes during pregnancy and lactation

• Calcium absorption is increased in pregnant women.

• The role of parathyroid hormone is unclear, since recent use of a more specific radioimmunoassay has cast doubt on previous reports of increased parathyroid hormone concentrations in pregnancy

During lactation………….

• Urinary calcium excretion is generally decreased.

• Increased calcium absorption may occur.

• No differences in fractional absorption have been found during established lactation between breast-feeding mothers and control subjects

Adverse effects of increases in calcium intakes

• Very high calcium intakes are believed to increase the risk of kidney stones

• Renal calculi occur in 1/1500 pregnancies

• The potential for urinary tract infection may be increased when urinary calcium excretion rises as a result of calcium supplementation

• In addition, increases in dietary calcium consumption have been associated with reduced absorption of other minerals

• such as

–Iron

–Zinc

–Magnesium

DISORDERS OF CALCIUM AND BONE

METABOLISM DURING PREGNANCY

&LACTATION

Osteoporosis in Pregnancy

• In such cases it is not possible to exclude the possibility that low bone density or skeletal fragility preceded pregnancy

• Osteoporosis in pregnancy usually presents in a first pregnancy at age 27-28 and there is no increased risk with higher parity

• Fractures tend not to recur in subsequent pregnancies

Other disorders• Low Calcium Intake

• Hypoparathyroidism

• Primary Hyperparathyroidism

Why you need calcium during pregnancy

• Baby needs calcium to build strong bones and teeth

• Grow a healthy heart, nerves, and muscles

• Develop a normal heart rhythm and blood-clotting abilities

• Reduce bone resorption