Vitamin D deficiency rickets: a problem for our times

Ben Wheeler

Bone needs an adequate supply of calcium and phosphate to mineralise properly. Failure of this mineral supply (for any reason) results in defects like osteomalacia (impaired mineralisation of the bone matrix) and osteoporosis (overall low bone mass). In children, inadequate mineralisation causes rickets. There are multiple causes of rickets, but the main one is vitamin D deficiency.

Rickets affects the open growth plate of a child’s long bones (the growth plate is closed in adulthood – which is why  we stop growing). This leads to the classic features of rickets: weakening of long bones, particularly those involved in weight bearing (hence the classic bowing of the legs); poor growth; delayed dentition; slowed motor development; and (rarely) pathological fractures. The most significant and dangerous feature of rickets is low blood calcium (hypocalcaemia), which is particularly common during periods of rapid growth such as infancy and early childhood.  Hypocalcaemia, which is the leading cause of death from rickets, leads to neuromuscular irritability which can cause tetany (muscle spasms) and, eventually, seizures.

The origins of the word “rickets” are somewhat unclear, but it may originate from the German “wricken” meaning “twisted”. The disease was first clearly described by English physicians Daniel Whistler in 1645, and Francis Glisson in 1650. However, rickets is recognisable in much earlier medical texts, such as Greek and Roman medical writings from the first and second centuries AD.

The so-called “first wave” of rickets dates from the seventeenth century, when the disease was prevalent in severely overcrowded and polluted industrial cities. Despite excellent scientific descriptions of the disease, its aetiology remained poorly understood and the rationale of potential treatments poorly validated. Glisson, for example, apparently suggested splinting, cautery, and pendulous suspension of the infant to help straighten out crooked bones.

It was not until the early twentieth century, when Edward Mellanby discovered a new vitamin (the fourth to be found), subsequently named “vitamin D” by Elmer McCollum, that a proper scientific understanding of the basis of rickets could begin.

Among the things we now know about vitamin D is that it is less efficiently metabolised from sunlight by those with darker skin. Therefore those with dark skin who live in less sunny climates are more at risk of vitamin D deficiency than those with pale skin. Indeed, the body’s thirst for vitamin D is the leading theory in accounting for the evolution of human skin colour from universally dark to a range of dark to pale. The theory is supported by archaeological evidence from the far north of Greenland, in which a colony of settlers appears to have become extinct secondary to gross pelvic deformities from osteomalacia.

In 1917, Alfred Hess, a paediatrician and nutrition researcher, was among pioneers who successfully advocated the use of cod liver oil (now known to be rich in vitamin D) in an at-risk black community. Interestingly, Hess also made observations about possible risk factors, noting the seasonal variation of rickets, and an apparent increased risk from  unsupplemented breastfeeding. His findings have since been confirmed in multiple recent studies, including some of our own from the University of Otago.

Despite these advances in knowledge and treatment, rickets continued to be common during the early twentieth century. A local illustration of how common rickets was at this time comes from a 1936 study of rickets in Sydney by K. Maddox. Maddox identified rickets in 52% of 218 infants reviewed in the outpatient department of the Renwick Hospital for Infants. He also offered some excellent advice on preventing rickets, much of which remains applicable today:

1. Public education in the dangers to the child of an ill-balanced diet in the mothers as regards vitamin content during pregnancy and lactation….;
2. a stronger insistence on daily exposure to the half-naked child to the direct rays of the morning sun;
3. the routine provision to all outpatients of a stronger preparation of cod-liver oil…

Use of cod liver oil and food fortification strategies (including increased use of infant formula) led to a decrease in rickets over the next few decades. However, increasing immigration to Europe and England of dark-skinned individuals from equatorial regions (e.g. India/South Asia, and the West Indies) led to a “second wave” of rickets. Again, successful public health vitamin D supplementation campaigns targeting these new immigrants reduced the number of rickets presentations.

Unfortunately, we are now in a “third wave” of rickets. In part, this is caused by lack of exposure to sunlight, due to modern lifestyles and sun avoidance measures, as well as our short memories for illness from the past. In addition, most people are probably unaware of existing public health policies for vitamin D supplementation to at-risk groups.

If we are to successfully prevent the many new cases of vitamin D deficiency rickets occurring in New Zealand children each year, more work is required to promote supplementation and food fortification strategies, particularly for children younger than 3 years, and especially those with any of the following risk factors: dark skin (especially those of South Asian and African descent), exclusive breastfeeding, and living in the South Island of New Zealand.

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Dr Ben Wheeler is a Paediatric Endocrinologist and Senior Lecturer working in Children’s Health at the Dunedin School of Medicine and Southern District Health Board.  He has particular clinical and research interests in paediatric aspects of bone disease, nutrition, and diabetes.

Sources:

• Maddox K. Rickets in Sydney, Australia. Arch Dis Child 1932;7(37):9-24
• Wheeler BJ, Taylor BJ, de Lange M, et al. A Longitudinal Study of 25-Hydroxy Vitamin D and Parathyroid Hormone Status throughout Pregnancy and Exclusive Lactation in New Zealand Mothers and Their Infants at 45 degrees S. Nutrients 2018; 10(1) doi: 10.3390/nu10010086[published Online First: Epub Date]|.
• Wheeler BJ, Dickson NP, Houghton LA, Ward LM, Taylor BJ. Incidence and characteristics of vitamin D deficiency rickets in New Zealand children: a New Zealand Paediatric Surveillance Unit study. Australian and New Zealand journal of public health 201515