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. 1998 May 30;316(7145):1671. doi: 10.1136/bmj.316.7145.1671a

Are sex and death related?

Study failed to adjust for an important confounder

David Batty 1
PMCID: PMC1113245  PMID: 9603760

Editor—Davey Smith et al report a significant inverse relation between frequency of orgasm and mortality due to all causes and coronary heart disease in men; however, a failure to adjust for the energy expended during sexual activity may be a weakness of their work.1 The intensity level of sexual activity is equivalent to that of leisurely walking or strolling,2 and an increasing level of energy output, even when amassed during walking, is independently associated with a decreased risk of all cause mortality.3 This failure to adjust for the energy cost of sexual activity may be amplified if, as seems plausible, the more sexually active individuals have a stronger disposition to physical activity per se than their less virile counterparts.

References

  • 1.Davey Smith G, Frankel S, Yarnell J. Sex and death: are they related? Findings from the Caerphilly cohort study. BMJ. 1997;315:1641–1645. doi: 10.1136/bmj.315.7123.1641. . (20-27 December.) [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 2.Ainsworth BE, Haskell WL, Leon AR, Jacobs DR, Montoye HJ, Sallis JF, et al. Compendium of physical activities: classification of energy costs of human physical activities. Med Sci Sports Exerc. 1993;25:71–80. doi: 10.1249/00005768-199301000-00011. [DOI] [PubMed] [Google Scholar]
  • 3.Hakim AA, Petrovitch H, Burchfiel CM, Ross GW, Rodriguez BL, White LR, et al. Effects of walking on mortality among nonsmoking retired men. N Engl J Med. 1998;338:94–99. doi: 10.1056/NEJM199801083380204. [DOI] [PubMed] [Google Scholar]
BMJ. 1998 May 30;316(7145):1671.

Study did not treat sexual behaviour with the importance it deserves

Agnes Ayton 1

Editor—The article by Davey Smith et al on sexual behaviour and mortality was a disappointment.1-1 The topic is important, and the results should at least be correct. I was surprised by the simplistic design, the mechanical interpretation of the results, and the selective use of references—even from the Holy Bible.1-2 Although long term follow up studies have to cope with shifts in medical thinking by the time of publication, this should have been addressed in the discussion. Even in the late seventies, during the time of the study’s design, psychological understanding of human sexuality was rather more complex than the authors imply. Firstly, not even minimal information on partners or relationships was included. Indeed, marital status was not mentioned and they gave no reason for this, despite numerous published studies on the relation between mortality and marital status before and since the seventies.1-3,1-4 It is likely that those men who had regular sexual activity in late middle age were either married or in long term relationships. The greater longevity of married compared with unmarried people has been shown repeatedly1-5 and this might be an important confounding factor. Secondly, it was naive to use the term sexual intercourse and orgasm interchangeably. If the authors were mainly interested in the health effect of orgasm, as a purely biological phenomenon, surely masturbation should not have been ignored. Thirdly, it is unlikely that sexual behaviour is static. As Hotopf and Wessely pointed out in their comment, sexual activity is influenced by age, health factors, and psychopathology.1-1 To these might be added changes in relationships, loss of spouse etc, which were not addressed, implying that the authors believe one self report measure is adequate to describe a person’s sexual activity during an entire lifetime, or at least from the age of 45 to death. Given these shortcomings, the authors should have been more cautious in their conclusions. The only message from this study is that the topic needs further (and more sophisticated) investigation. Inventing new health promotion slogans with numerical imperatives would be premature and should certainly be withheld.

References

  • 1-1.Davey Smith G, Frankel S, Yarnell J. Sex and death: are they related? Findings from the Caerphilly cohort study. BMJ. 1997;315:1641–1645. doi: 10.1136/bmj.315.7123.1641. . [With commentary by M Hotopf and S Wessely.] (20-27 December.) [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 1-2.Holy Bible. I Corinthians vii, 2-5.
  • 1-3.Berkson J. Mortality and marital status: reflection on the derivation of etiology from statistics. Am J Public Health. 1962;52:1318–1329. doi: 10.2105/ajph.52.8.1318. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 1-4.Goodwin JS, Hunt W, Key R, Samet JM. The effect of marital status on stage, treatment, and survival of cancer patients. JAMA. 1987;258:3125–3130. [PubMed] [Google Scholar]
  • 1-5.Chandra V, Szklo M, Goldberg R, Tonascia J. The impact of marital status on survival after myocardial infarction: a population based study. Am J Epidemiol. 1983;117:320–325. doi: 10.1093/oxfordjournals.aje.a113544. [DOI] [PubMed] [Google Scholar]
BMJ. 1998 May 30;316(7145):1671.

Author’s reply

George Davey Smith 1

Editor—Our report on the association between sexual behaviour and mortality was intended to illustrate the findings that associational epidemiological studies can produce.2-1 This information adds to earlier publications on the subject,2-2 which we did make clear in the discussion. The findings have interest beyond this, however, and we would welcome further investigations. We agree with Batty that attention should be paid to physical activity, but conceptual clarity needs to be maintained when this is done. Batty states that we failed to adjust for physical activity, which he considers an important confounder. It is possible that men engaging in lots of sexual activity also participate in other forms of physical activity. Adjusting for energy expended during sexual activity, as suggested by Batty, would not be adjusting for confounding as the physical activity involved in sexual encounters could be the protective factor and, therefore, an integral part of the exposure. Investigation of this issue would be complex. Although Batty explains that the exertion of sexual activity is equivalent to that of leisurely walking or strolling, this would be different for adventurous couplings.

Our article was intended to fit in with the festive cheer of the BMJ2-3,2-4 and to provide an introduction to associational findings in epidemiological studies. Ayton has missed both these points. The majority of our men were married and the results were identical if we restricted the analysis to married men. Our reference to health education was intended to be ironic, not least because the benefits exceeded those anticipated with most established health promotion programmes. Some readers obviously missed this mild mischief. In future, to spare disappointment at the end of the year perhaps Ayton should avoid the Christmas BMJ.

References

  • 2-1.Davey Smith G, Frankel S, Yarnell J. Sex and death: are they related? Findings from the Caerphilly cohort study. BMJ. 1997;315:1641–1645. doi: 10.1136/bmj.315.7123.1641. . (20-27 December.) [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 2-2.Davey Smith G, Phillips AN, Neaton JD. Smoking as “independent” risk factor for suicide: illustration of an artefact from observational epidemiology? Lancet. 1992;340:709–712. [PubMed] [Google Scholar]
  • 2-3.Cleare AJ, Wessely SC. Just what the doctor ordered—more alcohol and sex. BMJ. 1997;315:1637–1638. doi: 10.1136/bmj.315.7123.1637. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 2-4.White IR, McKee M. Festive cheer for all? BMJ. 1997;315:1638–1639. doi: 10.1136/bmj.315.7123.1638. [DOI] [PMC free article] [PubMed] [Google Scholar]

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