Association between body height and chronic low back pain: a follow-up in the Nord-Trøndelag Health Study

Introduction

Chronic low back pain (LBP) is a common disorder that has been associated with several predisposing factors. It has been difficult to identify the cause of non-specific LBP, and the onset of pain is most likely due to a complex interaction between environmental and genetic factors. It has been shown that a large body mass index (BMI) predisposes to LBP,^{1 2} but the association between body height and LBP has not been studied extensively. Body height is most likely influenced by genetic disposition, but circumstances during fetal development or in childhood, malnutrition, previous diseases and psychosocial factors are also important.³ In women, a large body height is associated with increased risk of several diseases, such as cancer of the ovaries^{4 5} and breast.⁵ By contrast, coronary artery disease is associated with short height.⁶

Earlier studies have shown conflicting evidence on the potential association between body height and LBP, and whether there are gender differences, but it is not clear whether all studies adjusted properly for BMI or body weight. Thus, body height has been found to be positively associated with the prevalence of LBP in both genders in young people.⁷ However, in a population study of adults over a 40-year age span, the risk of LBP was increased among tall men, but was not associated with body height among women.⁸

Although adult body height is hardly a factor that can be influenced, it is important to look at this variable for understanding the interplay between risk factors in explaining the causes of LBP. In this study, we consider the effect of body height on the development of LBP among adults, in an 11-year follow-up study based on data from two large health surveys in Norway.

Methods

Results

Among participants included in the analysis who did not report chronic LBP at baseline, a total of 10 059 women and 8725 men, altogether 2006 women and 1224 men experienced chronic LBP at the end of follow-up. Among participants in the analysis who reported chronic LBP at baseline, a total of 3883 women and 2662 men, altogether 2319 women and 1269 men experienced chronic LBP at the end of follow-up (table 1). Online supplementary tables S1 and S2 describe the distributions of covariates among women without LBP at baseline and online supplementary tables S3 and S4 describe the corresponding distributions among men.

The risk of LBP increased with increasing body height among women not suffering from LBP at baseline (table 1). No definite tendency was found among men without LBP at baseline, but the highest risk was seen among men ≥185 cm. No clear tendencies could be found among women or men who experienced LBP at baseline.

Among women without LBP at baseline, a weak positive association between body height and LBP was suggested with adjustment for age only, with very similar results after additional adjustment for BMI (table 2). With complete adjustment, the association became stronger and statistically significant (RR per 10 cm 1.09 (95% CI 1.01 to 1.17)). Risk estimates increased gradually along with increasing categories of height (table 2). There was no significant deviation from linearity (p=0.48). Among men, no significant associations with body height were seen, even after complete adjustment. Nevertheless, in the group of the tallest men, the risk estimate was increased, especially with complete adjustment.

Table 3 shows results from the continuous analyses within categories of age and BMI at baseline. No significant differences were observed between effects in age groups or categories defined by BMI. The risk ratios for women suggested positive associations within each age category and within each category of BMI. For men, modest positive associations were suggested in the lowest groups of age. In men with BMI ≥30, a more pronounced positive association was found. The overall analyses were also carried out with more detailed adjustment for BMI in five categories, and the results were essentially unchanged.

Among those suffering from LBP at baseline, no linear relations were found between height and recurrence of LBP after 11 years, either among women (RR per 10 cm 1.04 (95% CI 0.99 to 1.09)) or men (RR per 10 cm 0.95 (95% CI 0.89 to 1.02)).

Discussion

In this large population-based 11-year follow-up study, an association between body height and LBP was found in women without LBP at baseline, within the ordinary limits of uncertainty set by statistical procedures. Adjustment for BMI had hardly any influence on the association that was observed in women with high as well as low BMI at start of follow-up. It is therefore unlikely that the association with body height could be caused by an effect of increased body weight among tall women. Overall adjustment for other risk factors was still essential for detecting the relationship with body height. The magnitude of the association was modest. For example, for a woman 180 cm tall compared to the population average of 165 cm (see online supplementary table S1), the model based on height as a continuous variable predicts a 14% increase in risk. However, only 0.6% of the female population had a height of 180 cm or more, so for the great majority of women the increase is of minor concern.

On the basis of our data, it is not possible to infer that body height in men influences the risk of subsequent LBP. The width of the CIs determined makes it unlikely, however, that any real association is very strong. Our results are still consistent with an increased risk of LBP among men who are 185 cm or taller.

A strength of this study is the follow-up over a long period of time with a large number of participants recruited from an entire county. Measurements of height and weight were probably quite accurate. Although response rates were relatively high in the HUNT2 survey, the response was lower in the subsequent HUNT3 survey, and part of our cohort was lost during follow-up. We could not demonstrate that participation was substantially different in any particular group of body height, but participants without LBP at baseline subsequently lost to follow-up had somewhat higher systolic blood pressure, experienced less physical activity, were more often smokers and had less education (see online supplementary tables S1–S4). The same tendencies were found among participants with baseline LBP (results not shown).

One limitation of this study is the reliance on the information on pain collected in the questionnaires at baseline and at the end of follow-up. No further information was available about the medical history of back pain in each respondent, or about pain occurring in the intervening 11-year period. No detailed check of back status was made at the clinical examinations, and the pain intensity was not recorded. Some participants may have suffered from disc degeneration or herniation, or from osteoporosis or fractures and some may have experienced LBP as part of other conditions such as malignant disorders or inflammatory joint disease.¹² Although no age interaction was demonstrated in this study, the participants displayed substantial age differences, which makes it likely that the LBP recorded has many different sources.¹³ Thus, it is difficult to say whether the association observed with height among women represents a stronger, more specific relationship with a particular subgroup of the LBP cases, or if it simply reflects a general weak relationship.

It is not clear whether all previous studies of associations between body height and LBP were carried out with sufficient adjustment. An extensive cross-sectional study of Israeli military recruits found body height to be positively associated with the prevalence of LBP in both sexes,⁷ with ORs of 1.8 and 2.1 comparing extreme quintiles in women and men. However, adjustment was not possible for many potential risk factors. In a relatively large cross-sectional study from the Netherlands,¹⁴ an inverse association largely disappeared after adjustment for age, smoking and education. In a cross-sectional Japanese study of those who worked sitting down, those who were at least 170 cm tall carried a RR of about 1.4 compared to those who were 160–169 cm.¹⁵ In a British retrospective study of lifetime risk of LBP, men with a height of 184 cm or more had double the risk of those who were 170 cm or shorter.⁸ No association was seen among women. A British 1-year follow-up study of general practice populations found no clear evidence of an association in either gender.¹⁶ Height more than 180 cm was a risk factor for sciatica, but not for LBP without sciatica, in a 2-year follow-up of French men.¹⁷ In a large Finnish population-based follow-up study, a body height of at least 180 cm for men and 170 cm for women was a predictor of being diagnosed with herniated lumbar intervertebral discs.¹⁸ Another Finnish study also showed greater body height among patients undergoing surgery for disc herniation.¹⁹ In a large French prospective study, being tall (≥178 cm) was a predictor for back surgery among men.²⁰

The overall impression of the existing evidence is that most data sets either support a positive association between body height and risk of LBP, or that essentially no association could be established. In some cases, the associations reported seem remarkably strong in comparison with our estimates. Some discrepancies may be caused by different adjustment for other risk factors. In view of the relatively strong association between BMI and risk of LBP,^{1 2} adjustment for body size may be particularly important. Some apparent inconsistencies may also be due to different study designs, although LBP, the disorder under study, would hardly be expected to affect body height, so cross-sectional studies should be fairly reliable. It is also possible that publication bias may have affected studies finding weak or no associations with height, so that studies reporting strong relationships are over-represented in the literature.

By contrast with results concerning the association between BMI and LBP, our findings have no essential implications for clinical work or for public health. As the aetiology of this common disorder is largely unknown, it is still essential to investigate potential relationships with readily measurable risk factors such as height. Both the positive association with BMI and the weak association seen with height among women in this study indicate that a large body size, overall, may increase the total risk of LBP.

There is no obvious causal explanation for the association observed in women between LBP and body height, although tall people may be exposed to other mechanical issues, both anatomical and stress-related. There are indications that growth in adolescence may be related to LBP at a young age.²¹ A correlation between body height and facet joint asymmetry in patients with disc herniation has been reported.²² Social factors are significant for both height²³ and LBP. For other diseases with established associations with body height, as for certain cancers, the explanatory mechanisms have not been clarified. Hormonal factors may be significant, perhaps in relation to gender differences. The inverse association between height and coronary artery disease has partly been explained by an adverse lipid profile in short people,⁶ but this explanation seems less relevant for a positive association such as that observed with LBP, and, in any case, relationships between lipid levels and risk of LBP are not very strong.¹¹ Future studies of LBP in adulthood should also take into account data on the development of body height in childhood and adolescence.

Conclusions

In this large population-based study, we found that women with body height of at least 170 cm, who did not experience LBP at baseline, had 19% increased risk of LBP compared to women with body height less than 160 cm. This may reflect mechanical issues or indicate a hormonal influence.