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Epidemiology:
doi: 10.1097/01.ede.0000210245.97152.54
Letters

Birth Weight and Blood Pressure in Spouses

Olesen, Anne Vingaard; Parner, Erik Thorlund; Overvad, Kim; Olsen, Jørn

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Institute of Public Health; Department of Epidemiology; University of Aarhus; Aarhus, Denmark; avo@soci.au.dk (Olesen)

Institute of Public Health; Department of Biostatistics; University of Aarhus; Aarhus, Denmark (Parner)

Department of Clinical Epidemiology; Aarhus University Hospital; Aarhus, Denmark (Overvad)

The Danish Epidemiology Science Centre at the Institute of Public Health; University of Aarhus; Aarhus, Denmark; UCLA School of Public Health; Department of Epidemiology; Los Angeles, California (Olsen)

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To the Editor:

Low birth weight is correlated with high adult blood pressure according to the programming hypothesis,1–3 but the estimated effect is small4 and may even be confounded by social conditions or lifestyle factors.3,5

We studied the association between birth weight and blood pressure in couples to adjust for the social conditions that couples share. We randomly selected 1000 cohabiting couples, 50 to 65 years of age, from the Danish cohort study Diet, Cancer and Health. Using the place and date of birth, and names as identifiers, we located each person's birth record in the state archive; these midwife records include data on birth weight. If we could not match by one surname (maiden name) and place of birth for both partners, the couple was excluded from further analysis. We extracted data on midlife systolic and diastolic blood pressure (SBP and DBP) from the health examination at recruitment to the cohort study. Data were analyzed in a mixed model of 2 linear regression equations allowing for dependence between measurements from spouses.6 Analyzing husband and wife jointly allows for adjustment for latent lifestyle factors.

We located 1670 of the 2000 individuals with birth data (84%). The midwife records of the 330 remaining persons were either missing or too ambiguous for identification. Among the 1670 persons with midwife data, both partners' data were available in 472 couples.

Table 1 shows the slope estimates of SBP and DBP on birth weight from several models. The confounder adjustment for both latent and fixed lifestyle covariates did not substantially change the effect of birth weight on SBP and DBP. Inclusion of current body mass index in the analyses also did not affect estimates.7,8

Table 1
Table 1
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Furthermore, we found an unexpected, relatively large positive correlation between the blood pressure of one spouse and the birth weight of the other. According to the data, a man with low birth weight will experience high SBP as seen in Figure 1. At the same time, his high SBP correlates with both high birth weight and high SBP of the wife. That is difficult to explain in causal terms. This unexpected pattern was present but less apparent for DBP.

Figure 1
Figure 1
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These estimated associations could be the result of chance. Otherwise, we speculate whether selection of spouses or effect modification by lifestyle or treatment of high blood pressure is at work. We recommend that other spouse data are used to see whether our findings can be replicated.

The proportion of couples with missing birth data either for one or both partners was large but most likely unrelated to the hypothesis under study. Data were missing when midwife records were simply lost in the archive and for persons born on a day when a midwife had more than one delivery of mothers with the same surname. None of these conditions should cause selection bias, except by chance. Birth weight and outcome data were collected independently, which makes differential misclassification unlikely.

Our objective was to put the programming hypothesis on birth weight and adult blood pressure to a critical test. We got results that corroborate the association, but the finding of a correlation between the blood pressure of one spouse and the birth weight of the other may also serve as a warning sign. One should be careful when interpreting results from 2 measurements made 50 years apart without much control of what took place in the time between.

For more details regarding this study, refer to the supplementary material available with the online version of this letter.

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ACKNOWLEDGMENTS

We thank Hanne Grand for patiently reading the midwife protocols. Thanks are also due to Anne Tjønneland and the staff at the Danish study Diet, Health and Cancer.

Anne Vingaard Olesen

Institute of Public Health

Department of Epidemiology

University of Aarhus

Aarhus, Denmark

avo@soci.au.dk

Erik Thorlund Parner

Institute of Public Health

Department of Biostatistics

University of Aarhus

Aarhus, Denmark

Kim Overvad

Department of Clinical Epidemiology

Aarhus University Hospital

Aarhus, Denmark

Jørn Olsen

The Danish Epidemiology Science Centre at the Institute of Public Health

University of Aarhus

Aarhus, Denmark

UCLA School of Public Health

Department of Epidemiology

Los Angeles, California

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REFERENCES

1. Barker DJP. Mothers, Babies, and Disease in Later Life. London: BMJ; 1994.

2. Davey Smith G, Stserne J, Tynelius P, et al. Birth weight of offspring and subsequent cardiovascular mortality of the parents. Epidemiology. 2005;16:563–569.

3. Koupolová I, Leon DA, Vågerö D. Can confounding by sociodemographic and behavioural factors explain the association between size at birth and blood pressure at age 50 in Sweden? J Epidemiol Community Health. 1997;51:14–18.

4. Huxley R, Neil A, Collins R. Unravelling the fetal origins hypothesis: is there really an association between birthweight and subsequent blood pressure? Lancet. 2002;360:659–665.

5. Forsdahl A. Are poor living conditions in childhood and adolescence an important risk factor for arteriosclerotic heart disease? Br J Prev Soc Med. 1977;31:91–95.

6. Skrondal A, Rabe-Hesketh S. Generalized Latent Variable Modelling. Boca Raton, FL: Chapman & Hall/CRC; 2004;49–53.

7. Tu Y-K, West R, Ellison TH, et al. Why evidence for the fetal origins of adult disease might be a statistical artefact: the ‘reversal paradox’ for the relation between birth weight and blood pressure in later life. Am J Epidemiol. 2005;161:27–32.

8. Rich-Edwards JW, Kleinman K, Michels KB, et al. Longitudinal study of birth weight and adult body mass index in predicting risk of coronary heart disease and stroke in women. BMJ. 2005;330:1115–1118.

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© 2006 Lippincott Williams & Wilkins, Inc.

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