Bone health, Calcium, and Vitamin D

  • BONE HEALTH
  • KEY POINTS
    • Calcium, vitamin D, and physical activity are the three pillars of optimizing peak bone mass.
    • French recommendations for vitamin D supplementation have just been updated: supplementation of 400 to 800 IU/d in infants and children aged 0 to 18 years throughout the year, regardless of the type of breastfeeding and skin color in children under two years.
    • Doses in children over two years of age with risk factors for vitamin D deficiency (dark skin, obesity, vegan diet, lack of sun exposure) should be doubled.
    • The use of vitamin D in the form of food supplements is prohibited.
    • Parents’ use of self-medication of dietary supplements should be systematically investigated before any prescription of vitamin D in drug form.
    • 25(OH)D measurement has no place in the management of vitamin D supplementation in children in the general population
    • Calcium intakes vary with age.
    • Blood calcium levels are not a good reflection of calcium intake; in situations of profound and prolonged calcium deficiency, the bone becomes the body’s primary source of calcium.
    • Calcium deficiency is common in adolescents.
    • One must beware of profound calcium deficiency in the case of a vegan diet.

Bone mass is created for 90% during the first two decades, so it is fundamental to ensure that children have an adequate vitamin D and calcium intake.

Vitamin D
Reminder of physiology

Vitamin D is a hormone synthesized under the action of certain ultraviolet rays. It is rarely found in the diet (fatty fish, artificially fortified dairy products).

It exists in two primary forms :
– storage form: 25(OH) vitamin D3, 25(OH)D or calcidiol ;
– active form: 1,25(OH)2 vitamin D3, 1,25-D or calcitriol.

It plays a significant role in growth and bone quality.

It allows the maintenance of phosphocalcic homeostasis by :
– Stimulating intestinal absorption of calcium and phosphorus to maintain normocalcemia and adequate bone mineralization;
– Stimulation of tubular calcium reabsorption
– Inhibition of the synthesis of parathormone (PTH), a hypercalcemic and phosphatizing hormone.

It is a hormone with a beneficial effect on overall health :
– Anti-infectious
– Anti-inflammatory
– Anti-inflammatory
– Anti-tumor
– Cardiovascular protector
– Possibly beneficial for the psyche and neuronal development.

Supplementation recommendations for the general pediatric population

The recently updated French recommendations for vitamin D supplementation :
– Concern all children
– Propose a supplementation of 400 to 800 IU/d for infants and children aged 0 to 18 years throughout the year
– Emphasize that these intakes should be doubled in children over two years of age if there are risk factors for vitamin D deficiency :
* Dark skin
* Obesity,
* Lack of sun exposure,
* Vegan diet.

How to choose a supplement?
Hydroxylated derivatives : alfacalcidol, calcitriol, calcidiol
They are not suitable for preventive supplementation and are strictly reserved for therapeutic use.

Vitamins D2 and D3
– They represent the reference in the general population.
– Their bioavailability and half-lives are different: the half-life of D2 is less than that of D3; in the case of intermittent supplementation, D3 should therefore be preferred.

Risks with food supplements
– Overdosing in vitamin D and calcium because the concentrations are high: 500 to 1,000 IU of vitamin D in 1 drop, sometimes even much more!
– Possibility of combining food supplements.
– Poor information for families and sellers because of the recent change in concentration of certain forms is a source of error.
– Existence of food supplements combining calcium and vitamin D, offered from the age of 3.
* The final doses are far higher than the recommended daily allowance (RDA) for the age, at least for the youngest children.
* The child’s nutritional calcium intake is not considered.
* The combination of vitamin D and calcium in high doses, therefore, increases the risk of hypercalcemia, but also hypercalciuria and secondary renal nephrocalcinosis/lithiasis, the incidence of which is known to be rising in pediatrics in France, probably due to nutritional factors.

To remember
– Thus, the prescription of vitamin D in food supplements must be proscribed.
– Vitamin D is a drug to be handled, which a doctor must prescribe.
– There is a risk of deficiency rickets and overdosing (increasing the risk of renal lithiasis), either through poor prescription or parental understanding.

CALCIUM

Intestinal absorption
– It is a passive paracellular absorption that is not saturable and an active transcellular intestinal absorption.
– The duodenum is the predominant site of expression of calcium transporters.
* The factors impacting absorption and, therefore bioavailability of dietary calcium are increased absorption :
Growth, calcium deficiency, lactose from dairy products, oxalate at deficient concentration, calcium from mineral waters ;
* Decreased absorption: oxalates and phytates found in certain vegetables, insoluble fibers in fruits and vegetables rich in uronic acids;
* Non-modification of intestinal absorption of calcium: lipids and proteins.

The major organs involved in calcium bioavailability are : intestine, bones and the kidney.

Urinary calcium excretion is physiologically lower in children than adults due to growth, especially in calcium deficiency situations.

In the case of severe and prolonged calcium deficiency, the bone becomes the primary provider of calcium for the body.

Deficiency
Deficiency is defined as a prolonged intake of calcium below the recommended intake for the age

Consequences
– These are similar to those of vitamin D deficiency, i.e., intestinal absorption of calcium is insufficient to meet the body’s needs despite reduced renal excretion of calcium.
– The deficiency is associated with a secondary increase in the level of 1,25(OH)2D contributing to the maintenance of serum calcium at the expense of bone mineralization.
– A low calcium diet is associated with increased PTH in children with 25(OH)D > 50 nmol/L [10].
– Chronic dietary calcium deficiency and increased PTH/1,25(OH)2D impair cartilage and bone mineralization.
– Increased PTH levels inhibit tubular reabsorption of phosphate, contributing to hypophosphatemia and a further defect in bone mineralization.

Conclusion
New French recommendations on vitamin D supplementation and optimization of calcium intake in children aged 0 to 18 years have just been published by a multidisciplinary working group, including a section for premature infants.

Vitamin D remains a drug that a physician must prescribe.

The prescription of vitamin D in food supplements should be avoided.

Research into the use of self-medication food supplements by parents should be systematically carried out before any prescription of vitamin D in medicinal form.

Calcium deficiency is common in adolescents, and one should beware of profound calcium deficiency in the case of a vegan diet.

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