Fifty-six cases (34 males, 60.7%) of severe, deforming JSF were identified from the 1263 [691 females (54.7%) 88.0% of the entire village population] that were available for musculoskeletal examination. This represented a prevalence of 4.4% (95% CI, 3.3–5.6). Twenty-four cases of JSF (contained within 10 families) had at least one sibling who was also affected. The prevalence in males was 6.2% (95% CI, 4.2–8.2) and in females 3.1% (95% CI, 1.8–4.4). The age of the cases of JSF identified ranged from 2 to 30 years; their mean age was 12.0 years (95% CI, 10.1–13.9). Age specific prevalence rates in Table 2 show that JSF was most common in 10–14 year olds. . . .

In the multivariate analysis, a number of risk factors for JSF emerged. As expected, predominantly drinking well water (rather than low-fluoride piped or ground water) was a significant independent risk factor, which is modifiable. As has been previously reported in relation to DF, magadi consumption, particularly consumption regularly throughout childhood, seems to be an important independent risk factor contributing to the development of JSF. Other dietary factors may be of importance in the development of deforming disease, either because they increase the load of fluoride that the body is exposed to, or provide a protective effect. When taking dietary histories, it became clear that the staple diet in Tindigani was ‘ugali’, a maize-based porridge that is used from weaning onwards. In some families, this was served with bananas (particularly during weaning), spinach or beans but only on an infrequent basis. Being weaned on bananas came out as an independent protective factor. Although the reasons for this are not entirely clear, it may reflect the relatively high calcium levels found in bananas. It is also possible that children who were weaned on bananas consequently consumed less ‘ugali’ during early life. As ‘ugali’ is made with boiling water, it is likely to have a relatively high-fluoride content.

In univariable analysis, eating both beans and spinach on a regular basis (more than once a week) was protective. This may reflect beans being one of the few regular sources of protein (meat was eaten on special occasions only) and also may represent a marker of better nutritional status overall. Owing to the difficulty, recalling exact diet over a long period of time, it was only possible to obtain a rough estimation of calcium and protein intake, but many families (particularly amongst the cases) were essentially only eating ‘ugali’ and, therefore, likely to be calcium and protein deficient. We do not think that vegetables themselves would have been a major source of fluoride. The people in the village were of predominantly Maasai tribal origin. They raised animals and did not generally grow their own vegetables. Vegetables were bought locally on a very irregular basis, and we cannot be sure whether the water used to irrigate these vegetables was from high-fluoride containing wells.

Low BMI also emerged as a significant predictor of outcome, although whether a low BMI represents a marker of poor nutritional status that is a causative factor in developing JSF or whether low BMI is a consequence of having SF remains unclear. Those who drank more tea per day had an increased risk of JSF. This is most likely to be due to increased concentration of fluoride ion, which occurs during the boiling of water and also the possibility of high concentrations of fluoride in the tea leaves used (Gulati et al. 1993). The tea consumed was regionally grown black tea. Some of these factors may help explain why there is variation in the penetrance of skeletal changes seen in exposed populations.