Back pain and risk of fatal ischaemic heart disease: 13 year follow up of Finnish farmers
BMJ 1994; 309 doi: https://doi.org/10.1136/bmj.309.6964.1267 (Published 12 November 1994) Cite this as: BMJ 1994;309:1267
- J Penttinen
- Accepted 16 June 1994
In the early 1980s some authors found an association between cardiovascular risk factors, especially smoking, and back pain.1 Quite recently Kauppila and Tollroth reported an association between history of back pain and atherosclerotic lesions of lumbar arteries in cadavers. They suggested that back pain could be an early symptom of atherosclerosis.2 Prospective studies concerning mortality related to back pain have not been published previously. My purpose was to find out whether patients reporting back pain have an increased risk of dying of ischaemic heart disease when compared with those who have no back symptoms.
Subjects, methods, and results
The basic population consisted of 8816 Finnish farmers who participated in a postal survey in November 1979 to January 1980. Those 3842 women and 3648 men who did not report any cardiovascular disease in the questionnaire (except haemorrhoids or varices) and who were 30-66 years old in 1980 were selected for the follow up study.
I included back pain and sciatica in the year before follow up as dichotomous variables. Sciatic pain was included only if the subject had had back pain. Smoking was included as one of three categories (current smoker, former smoker, and never smoked), body mass index (weight (kg)/(height (m)2)) as a continuous variable, and social status as one of three categories on the basis of the size of the farm. Mortality between 1 February 1980 and 31 January 1993 was determined from the register of the Social Insurance Institution of Finland. Copies of death certificates were obtained from the Finnish Statistics Bureau. The code numbers 410-414 of the International Classification of Diseases, ninth revision (ICD-9), were used for ischaemic heart disease as a cause of death. Other cardiovascular causes included the ICD-9 codes 390-459, excluding 410-414. I carried out cross tabulation analysis using the X2 test or Fisher's exact test. The adjusted relative risk was calculated by logistic regression analysis (EGRET).
The cross tabulation showed that men who were 30-49 years old and reported back pain during the preceding year at the beginning of follow up had a significantly increased risk of dying of ischaemic heart disease during the 13 years of follow up when compared with those of the same age with no symptoms (table). This result remained after adjustment for age, smoking, body mass index, and social status. The relative risk was 4.6 (P=0.04, 95% confidence interval 1.06 to 19.6) in the logistic model. The association between back pain and death from ischaemic heart disease was similar in those with and without sciatica. The risk of dying of other cardiovascular diseases was no higher in the group with back pain. For men aged 50 and over back pain did not precede death from ischaemic heart disease or any other particular disease during follow up. Smoking was significantly related to risk of death from ischaemic heart disease in men of every age. Body mass index or social status did not correlate with ischaemic heart disease at any age. In women no association between back pain and any vascular disease was found.
Age specific mortality (per 1000 people and 13 years) of men according to history of back pain
Comment
Mechanical reasons and disc degeneration have been proposed as the main causes of back pain. My results support the hypothesis that back pain in some cases may be an early manifestation of atherosclerosis. Anything causing or worsening local ischaemia of the lumber region may cause back pain. In a recent study of fire fighters in New York a strong association between smoke and first episode of back pain was found.3 So called unspecific back pain may often have a vascular basis, which may be atherosclerosis or any other defect causing temporary ischaemia.
According to a recent study back pain may be related to work in the same sense as angina pectoris is. The association between smoking and back pain has been found to depend on the job of the subject. There seems to be an association between smoking and back pain, however, only in physically demanding jobs.4 One should, however, be cautious in interpreting the observed association between smoking and back pain because, for example, pain in the extremities is more clearly associated with smoking than back pain.4
I found no relation between back pain and death from ischaemic heart disease in older men. One possible explanation is that people with chronic back pain tend to retire earlier from physically demanding work. According to former observations the risk of back pain increases until the age of 50 years and then decreases.5
To my knowledge, this is the first prospective study on the association between back pain and mortality. More research is needed to determine the validity of these results and to find out the character and mechanism of vascular back pain. If vascular reasons prove to be the usual causes of back pain, the diagnosis and care of chronic back pain will change drastically.
This study was supported by the Farmers' Social Insurance Institution of Finland. I thank Pentti Makela for his data processing work.