Bone growth and height gain – basics

How do bones get longer?

Soft bone development begins during pregnancy at 7 weeks, and is most active during the third trimester. After birth, the bones become hardened through a process called “ossification” [1]. Until then,  bones are mostly made of cartilage at birth, which is soft and rubbery.

In the long bones of the arms and legs, specific areas near the joints contain the most active areas of ossification. These areas are called growth plates. The bone cells that live there convert the calcium, phosphorus and other minerals taken from the baby’s diet into a cement-like substance called “bone mineral” (also called “matrix”).

Bone mineral is built-up a layer at a time across the width of the bone, making it gradually elongates. In the leg bones, this contributes to increasing height. This is most active in the first 5 years, and sometimes causes “growing pains”. Bone mineral is important because it enables the body to hold itself up as the baby gets older, especially after the first year, when they learn to walk.

At the same time, muscles get longer and stronger and perform physical functions in coordination with the skeleton. This also stimulates bone growth.

Why are calcium and phosphorus so critical for bone growth?

Calcium and phosphorus form part of a material called hydroxyapatite, which is the matrix part of bones. Breastmilk and cow’s milk are naturally occurring sources of calcium and phosphorus, in a  complexed with milk proteins. This is how the calcium and phosphorus are carried into the digestive system and absorbed across the intestine.

Some of the absorbed calcium also remains in a soluble form. This is used by bone cells to perform their ability to grow and produce matrix, as well as by muscles to grow and maintain their ability to get longer and contract. Calcium is a vital electrolyte required in every cell in the body, while phosphorus is equally important, because it is used in energy production and making new DNA.

What happens if calcium and phosphorus are lacking?

Undernutrition, either of mum during pregnancy and breastfeeding, or of the infant or child due to lack of the right levels and balance of nutrients can cause a calcium shortage. Breast milk doesn’t change its level of calcium very much, even when the mother doesn’t take in enough, because it starts to take it from mom’s own skeleton [2].

A children’s health report published by scientists in India, where childhood undernutrition and stunting (shortness for age) remains a huge problem, found that only 15.5% and 16.4% of infants aged 1-3 yr and children 4-6 yr, respectively, took in more than 70% of the recommended calcium intakes for those age groups [3].

Lack of calcium is one of the causes of rickets [4], a condition where bones remain in their soft form, and ossification is delayed. This means that as the body grows and gets heavier, the bones are less able to support body weight, so they start to bend, especially in the legs. This causes growth abnormalities and can affect height gain. Other parts of the skeleton affected include the spine.

Does adequate calcium help?

The short answer is, yes. Most of these benefits have been seen in South Asian and African countries, where child undernutrition, although it has declined, still hovers between 20-50% [5].

In one Nigerian study published in the New England Journal of Medicine, children with rickets from nutritional deficiency showed a restoration in their lower than normal calcium levels, by dietary replacement of calcium, after 12 weeks [6].