The Bergen Blood Pressure Study: Definition of Hypertensive and Normotensive Families Based on 27 Years' Follow-up

Weight gain and the risk of knee replacement due to primary osteoarthritis: a population based, prospective cohort study of 225,908 individuals

OBJECTIVE

To study the association between weight gain and the risk of knee replacement (KR) due to primary osteoarthritis (OA), and to evaluate whether the association differs by age.

DESIGN

225,908 individuals from national health screenings with repeated measurements of height and weight were followed prospectively with respect to KR identified by linkage to the Norwegian Arthroplasty Register. Cox proportional hazard regression was used to calculate sex-specific relative risks (RR) of KR according to change in Body Mass Index (BMI) and weight, corresponding analyses were done for age categories at first screening.

RESULTS

During 12 years of follow up, 1591 participants received a KR due to primary OA. Men in the highest quarter of yearly change in BMI had a RR of 1.5 (95% confidence interval (CI) 1.1-1.9) of having a KR compared to those in the lowest quarter. For women the corresponding RR was 2.4 (95% CI 2.1-2.7). Men under the age of 20 at the first screening had a 26% increased risk for KR per 5 kg weight gain, for women the corresponding increase was 43%. At older age the association became weaker, and in the oldest it was lost.

CONCLUSIONS

Weight gain increases the risk for later KR both in men and women. The impact of weight gain is strongest in the young, at older age the association is weak or absent. Our study suggests that future OA may be prevented by weight control and that preventive measures should start at an early age.

Beta-2 adrenoceptor genetic variation is associated with genetic predisposition to essential hypertension: The Bergen Blood Pressure Study

We tested the hypothesis that genetic variation in the beta-2 adrenoceptor gene is associated with a genetic predisposition to hypertension. Offspring of two hypertensive parents were compared with offspring of two normotensive parents. The subjects were participants of the Bergen Blood Pressure Study, where couples were recruited in 1963 to 1964 and re-examined in 1990. We studied offspring of those couples in which both partners were either hypertensive or normotensive in both examinations. Twenty-three hypertensive and 22 normotensive families met the inclusion criteria. DNA samples from the first born of hypertensive family-history offspring and normotensive family-history offspring were analyzed. We used multiplex sequencing and specifically examined the promoter and the N-terminal portion of the beta-2 adrenoceptor gene. We found four genetic variants: at position -47, a C-->T substitution in the 5' leader cistron causing an Arg-->Cys exchange, at -20, a T-->C substitution, at +46 an A-->G substitution leading to an Arg16-->Gly exchange, and at +79, a C-->G substitution leading to a Gln27-->Glu exchange. The frequency of the Arg16 allele was significantly higher in the hypertensive family-history offspring compared to normotensive family-history offspring (58% vs. 28% P < 0.011). We constructed haplotypes for the four intragenic variants and found significant linkage dysequilibrium. In particular, the 5' leader cistron mutant with the wild type alleles at the other loci was significantly more frequent in offspring of hypertensive parents, compared to offspring of normotensive parents. We also performed a relative risk analysis comparing the Gly/Gly, Arg/Gly, and Arg/Arg alleles, which implicated the Arg-containing allele. Finally, we analyzed the effect of genotype on blood pressure in the offspring. We found a significant step-wise effect for all four polymorphisms examined. Our data suggest that the Arg variant of the Arg-->Gly exchange is associated with parental hypertension and higher blood pressure values in this northern European population.

The Bergen Blood Pressure Study: prehypertensive changes in cardiac structure and function in offspring of hypertensive families

Cardiac morphology and function were determined by echocardiography in normotensive offspring of 23 hypertensive and 22 normotensive families. The family histories of hypertension or normotension were based on 27 years' observation of parental blood pressure. Pulsed Doppler and M-mode echocardiography were performed in standard views. Out of the total 109 offspring, 94 participated in the present study (age (mean +/- SD) 36 +/- 7 years). Left ventricular posterior wall thickness was higher in offspring of hypertensive than normotensive families (10.1 +/- 1.7 vs. 9.3 +/- 1.5 mm; p < 0.05). Offspring of hypertensive families had lower transmitral early/late peak flow velocities (p < 0.001) and higher transmitral late peak flow velocities (p < 0.001) than offspring of normotensive families, but the differences between groups became inconsistent after adjustment for confounding variables (including left ventricular structural parameters). On the other hand, the family history of hypertension was consistently associated with increased transmitral early peak flow velocity and increased transmitral acceleration and deceleration slopes p < 0.05), a pattern suggesting increased left ventricular stiffness. Increased posterior wall thickness and diastolic functional changes may indicate cardiac hypertrophy and decreased left ventricular compliance and precede the development of hypertension in offspring of hypertensive families.

The Bergen Blood Pressure Study: inappropriately low levels of circulating atrial natriuretic peptide in offspring of hypertensive families

Plasma atrial natriuretic peptide (ANP), plasma and 24-h urine catecholamines, plasma renin activity (PRA), and serum aldosterone were studied in offspring of hypertensive and normotensive families [n = 82; age 37 +/- 7 years (mean +/- SD)]. Despite higher age, higher blood pressure, and higher urine excretion of catecholamines--all of which are factors associated with increased ANP levels--the mean basal plasma ANP concentration tended to be lower in offspring of hypertensive than normotensive families. The same pattern was found in all age-tertiles, and the between-group difference was statistically significant in subjects aged 34-39 years (p < 0.01). Also, the family history of hypertension was associated with low ANP levels after covariate adjustment (p < 0.05). The 24-h urine excretion of epinephrine and norepinephrine tended to be higher in offspring of hypertensive than normotensive families while the morning venous plasma levels were similar. The ratio between venous plasma ANP and norepinephrine was lower in offspring of hypertensive than normotensive families (p < 0.05). PRA, serum aldosterone level, and 24-h urine excretion of dopamine did not differ significantly between groups. Inappropriately low basal plasma ANP concentrations and low plasma ANP/norepinephrine ratios may be related to the development of essential hypertension in offspring of hypertensive families.

The Bergen blood pressure study: sodium intake and ambulatory blood pressure in offspring of hypertensive and normotensive families

Sodium intake, estimated by the 24-h urine sodium excretion, was assessed in 39 offspring of hypertensive families and 37 offspring of normotensive families. The family history of hypertension or normotension was defined according to parental BP data from two surveys conducted 27 years apart. Urine-sodium excretion was similar in offspring of hypertensive and normotensive families, averaging 136 and 137 mmol/24 h, respectively. Monitored by non-invasive methodology in the urine sampling period, the average 24-h ambulatory blood pressure (BP) was approximately 10/10 mmHg higher in offspring of hypertensive than normotensive families. The clinically and statistically significant differences in BP between groups could not be explained by differences in sodium intake. After adjustment for confounding variables, the BP was not associated with the sodium excretion in the material as a whole or in either offspring group.

The Bergen Blood Pressure Study: blood pressure changes, target organ damage and mortality in subjects with high and low blood pressure over 27 years

Based on the Bergen population screening in 1963-64, 344 married couples (688 subjects), then aged 30-69 years, were included for studies in families with a history of hypertension or normotension. In 1990 430 subjects were available to a follow-up examination. The present paper describes 27-year mortality, blood pressure (BP) changes, cardiovascular disease and target organ damage in this population. In males who were hypertensive by the 1963-64 screening BP, the all-cause 27-year mortality was three times higher than in initially normotensive males (p < 0.05). From 1963-64 to 1990, the systolic BP was generally increased, whereas the diastolic BP was decreased in initially hypertensive and increased in initially normotensive subjects. In subjects who were hypertensive in 1963-64, the relative risk of hypertension in 1990 was more than seven times higher than in initially normotensive subjects (p < 0.05), cardiovascular events were reported more often (p < 0.001), and the mean electrocardiographic left ventricular voltage was higher (p < 0.01). Proteinuria was more frequent in initially hypertensive than normotensive males (p < 0.01). In summary, hypertension defined by a single BP recording at the 1963-64 screening was a risk factor for hypertension, cardiovascular morbidity and, for males, all-cause mortality 27 years later. With respect to offspring studies, our findings substantiate the classification of hypertensive and normotensive families. From 1963-64 to 1990, the BP status had changed in several couples, and the long observation period seems mandatory if a reliable definition of the family history of hypertension or normotension is to be obtained.