The skeleton of an infant showing signs of rickets. (IMAGE: Historic England)

Several previous ‘Science Notes’ have featured osteological analysis tangentially (see CA 337, 338, 342, and 344), but we have not explored it in depth – until now. This month’s column considers the effects of vitamin D deficiency, how it can be identified in skeletal remains, and what it can tell us about past populations.

We are probably all aware of vitamin D deficiency and the effects it can have on our health. While seasonal depression may be the biggest modern blight when this particular vitamin is lacking, in the past, when remedies were harder to come by than simply taking a supplement pill, the outcomes could be much more severe.

Vitamin D is essential for the metabolism of calcium and phosphorus, which are in turn necessary for adequate bone formation. When we lack the vitamin, our bones are not properly mineralised, making them softer and more pliable, and causing them to bend and/or fracture more easily. In children, while bones are still growing, this condition is called rickets; in adults, it is known as osteomalacia.

Deficiency can be caused by the body’s inability to metabolise vitamin D, but it is more frequently down to not acquiring enough of it. Ultraviolet (UV) light is the main way by which humans accumulate the vitamin, so insufficient exposure to sunlight is the most common cause of this problem. This means that people who live at higher latitudes are more prone to the condition, because in these areas sunlight is less intense.

Certain cultural norms can also lead to an increased prevalence of vitamin D deficiency. In the 19th century, rickets was common in cities and towns across central and northern Europe, largely due to the effects of the Industrial Revolution. Tall, closely spaced buildings in urban areas limited the amount of sunlight that reached ground level, and air pollution from industrial processes meant that the sunlight that did penetrate was of lesser potency. In more recent years, there has been an increase in vitamin D deficiency caused by children spending more time inside, and exacerbated by sunscreens that are so effective that little UV light can penetrate.

While the connection between the Industrial Revolution and vitamin D deficiency is well known, evidence from other periods has been less well studied. A recent investigation, from researchers at McMaster University in Canada and at Historic England, has helped to correct this by assessing the impact of vitamin D deficiency in the Roman Empire. The team collected data from 2,787 skeletons (1,143 children and 1,644 adults) interred in 18 different cemeteries and associated with 15 different settlements across the Empire, spanning the Mediterranean to northwestern Europe, and dating between the 1st and 6th centuries AD.

The leg bones (tibiae) of an adult in the study showing bowing likely caused by previous vitamin D deficiency. (IMAGE: Historic England)

The researchers assessed each skeleton for signs of vitamin D deficiency: evidence of rickets in children includes bowing and flaring of long bones and ribs. Bowing of the leg bones is particularly common (the leg bones of one Roman individual involved in the study are shown above; the skeleton of an infant that was also examined by the researchers is shown right), while bending of the arm bones can occur if a child was affected with the condition while they were still crawling.

In cases of active rickets, where the child still had the condition at the time of his or her death, porosity can also be seen in the growing surfaces of bone. Bending deformities may persist into adulthood, long after rickets has healed. The most consistent sign of vitamin D deficiency suffered in adult life is the presence of small fissure-fractures in the weakened bone, especially the ribs.

In total, the study found that 5.7% of juveniles were affected by rickets, while 3.2% of adults showed either healed rickets or osteomalacia. Perhaps unsurprisingly, most cases of vitamin D deficiency were identified in sites from more northern latitudes, indicating that reduced exposure to sunlight was indeed the main cause. In particular, among the juveniles, most of those affected were infants. It is thought that this increased prevalence of rickets may have been due to childcare practices – perhaps keeping the infants indoors, away from the cold, also limited their exposure to sunlight enough to cause them to become vitamin D deficient.

Going against the latitude trend, though, there was also an elevated frequency of rickets at the cemetery of Isola Sacra in Italy. This burial ground lay adjacent to the town of Ostia (at the mouth of the Tiber, near Rome), which was characterised by high-density housing provided by multistorey apartment blocks with only small windows – features that were not present in other sites used in the study. The researchers believe that these conditions may have blocked out enough sunlight to leave the town’s children at a heightened risk of rickets.

Overall, this study has demonstrated that while the Industrial Revolution may have marked the pinnacle of the condition, vitamin D deficiency was a significant problem 1,500 years earlier in the Roman Empire. Contributing factors probably included infant-care practices that, in more northerly locations, limited exposure to sunshine to a sufficient degree to cause rickets. In addition, Ostia’s dense occupation of multistorey blocks that prevented direct sunlight from reaching living quarters echoes a factor that would help to lead to the rise of rickets centuries later in the cities of the Industrial Revolution.

This article appeared in CA 348.

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