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R Jorde, KH Bonaa and J Sundsfjord

OBJECTIVE: To study associations between serum ionised calcium, serum parathyroid hormone (PTH) and blood pressure. DESIGN: A population based, cross-sectional study was used.Methods: Blood pressure, body mass index, serum ionised calcium and serum PTH were measured in 460 males and 486 females in the Tromso study in 1994/1995. None were on medication for hypertension. The data were analysed with a multiple linear regression model. RESULTS: When looking at subjects with serum ionised calcium<1.39mmol/l, there was a significant negative association (P<0.01) between serum ionised calcium and PTH. There was no association between blood pressure and serum ionised calcium. In both sexes there was a significant positive association between age and serum PTH (P<0.01). For women, but not for men, there was a significant positive association between serum PTH and systolic and diastolic blood pressure (P<0.01). Within each age group there was a difference in both systolic and diastolic blood pressure of 3-10mmHg between the upper and lower serum PTH halves of the female population. Females with hypertension had significantly higher serum PTH levels than the normotensive females (P<0.01). CONCLUSION: Serum PTH is strongly and positively associated with blood pressure in women.

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E Kamycheva, J Sundsfjord and R Jorde

OBJECTIVE: To study whether serum parathyroid hormone (PTH) and serum calcium are associated with body mass index (BMI), and their predicting role in obesity. DESIGN: Population based, cross-sectional study. METHODS: In 2001 a population-based health survey was held in Tromso, North Norway. Questionnaires on medical history and life-style factors were completed and anthropometric data were collected. Calcium and vitamin D intakes and a physical activity score were calculated. Serum calcium and PTH were measured in a subset of 3447 men and 4507 women. Pearson correlation and linear regression were used to evaluate associations between BMI, PTH and serum calcium, and logistic regression was used to test PTH and serum calcium as predictors of obesity and to calculate odds ratio. Relative risk was calculated using frequency tables. RESULTS: For serum calcium and PTH there was a significant positive relation to BMI in both genders (P<0.001), which to our knowledge has not previously been reported on the basis of a large epidemiological study. Age, low calcium and vitamin D intakes were explanatory variables for serum PTH. The highest quartile of serum PTH (>4.20 pmol/l) was a significant predictor for obesity (P<0.001) in both genders, adjusted for age, physical activity and serum calcium. Obesity rates were higher in those with PTH levels in the highest quartile compared with those in the lower quartiles, which resulted in a relative risk of 1.40 (95% confidence interval (C.I.) 1.20-1.60) for men and 1.48 (95% C.I. 1.31-1.67) for women. CONCLUSIONS: Serum PTH, adjusted for age, physical activity and serum calcium, is positively associated with BMI in both sexes, and serum PTH is an independent predictor of obesity in our statistical model.

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M Sneve, Y Figenschau and R Jorde

Objective

Investigate whether cholecalciferol supplementation leads to weight loss in overweight and obese adults.

Design

Randomized double blind clinical trial with 20 000 IU cholecalciferol twice a week, or 20 000 IU once a week plus placebo, or placebo twice a week, for 12 months. All subjects were given 500 mg calcium supplementation.

Methods

Four hundred and forty five healthy, overweight, and obese men and women (age 21–70 years, body mass index (BMI) 28.0–47.0 kg/m2). Body weight, fatness, and fat distribution parameters were measured by dual-energy X-ray absorptiometry and anthropometry, blood samples and 24-h urinary samples were collected.

Results

At baseline, there were no significant differences between the groups, but there was a significant inverse relation between serum 25-hydroxyvitamin D (25(OH)D) levels and BMI, and a significant positive association between calorie intake and BMI. Three hundred and thirty four subjects completed the study. During the study, there was no significant change in weight, waist-to-hip ratio (WHR) or percentage body fat in any of the groups, nor between them. Parathyroid hormone decreased and 25(OH)D increased significantly in both groups receiving cholecalciferol, and serum levels of 25(OH)D stabilized after 3 months. Serum calcium was unchanged in all groups. Urinary calcium excretion increased in all groups, but there was no significant difference between the groups. Weekly dosage of 20 000–40 000 IU cholecalciferol for 12 months was associated with a low risk of adverse effects, at least in overweight and obese adults living at latitude 70° N.

Conclusion

Significant weight reduction in overweight and obese subjects is unlikely to occur with cholecalciferol supplementation.

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R Jorde, F Saleh, Y Figenschau, E Kamycheva, E Haug and J Sundsfjord

Objective: Smoking is associated with reduced bone density and calcium absorption, and reduced serum levels of vitamin D. A compensatory increase in serum parathyroid hormone (PTH) would therefore be expected as a result of an altered calcium balance. However, reports on PTH levels in smokers are conflicting. As serum PTH levels give important information on the calcium balance, the PTH levels in smokers are of interest.

Subjects and methods: In the fifth Tromsø study, smoking status was recorded and serum PTH measured in 7896 subjects. Intakes of calcium and vitamin D were evaluated with a food-frequency questionnaire. In a follow-up study on 205 subjects, serum 25-hydroxyvitamin D, calcium absorption, and renal excretion of calcium were measured in addition.

Results: The serum PTH levels were significantly lower in smokers than non-smokers (3.1±1.4 vs 3.6±1.9 pmol/l in males; 3.1±1.5 vs 3.6±1.8 pmol/l in females (P < 0.001) after correcting for confounding variables, linear regression). In the smokers, there was no association between number of cigarettes smoked and serum PTH. One year after quitting smoking, serum PTH levels were similar to those of people who had never smoked. The smokers had significantly lower intake of vitamin D, lower serum levels of 25-hydroxyvitamin D and lower calcium absorption. The intake of calcium and the renal excretion of calcium were similar to that in non-smokers.

Conclusions: Smokers have lower serum PTH levels than non-smokers. This cannot be explained by the predictors of serum PTH measured in our study.

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J Svartberg, D von Muhlen, H Schirmer, E Barrett-Connor, J Sundfjord and R Jorde

OBJECTIVE: To test the hypothesis that lower endogenous testosterone levels are associated with higher blood pressure, left ventricular mass, and left ventricular hypertrophy. DESIGN: Population-based cross-sectional study. METHODS: Sex hormone levels, measured by immunoassay, anthropometric measurements and resting blood pressure were studied in 1548 men aged 25-84 Years; echocardiography was completed in 1264 of these men. Partial correlations and multiple regressions were used to estimate the associations between sex hormones, blood pressure and left ventricular mass by height. Analyses of variance and covariance were used to compare men with categorical hypertension and left ventricular hypertrophy. RESULTS: In age-adjusted partial correlations, total testosterone and sex hormone-binding globulin (SHBG) were each inversely associated with systolic blood pressure (SBP) (P<0.001). Men with categorical hypertension (SBP> or =140 or diastolic blood pressure (DBP)> or =90 mmHg) had lower levels of total and free testosterone and SHBG before (P<0.001, P=0.011 and P<0.001, respectively) and after (P<0.001, P=0.035 and P=0.002, respectively) adjusting for body mass index (BMI). Total testosterone and SHBG were each inversely associated with left ventricular mass (P<0.001), and men with left ventricular hypertrophy had significantly lower levels of total testosterone (P=0.042) and SHBG (P=0.006); these associations were no longer significant after adjusting for BMI. CONCLUSION: The results of the present study are consistent with the hypothesis that lower levels of testosterone in men are associated with higher blood pressure, left ventricular mass, and left ventricular hypertrophy. The reduced associations after adjusting for BMI suggest that the association of low testosterone levels with blood pressure and left ventricular mass is mediated by obesity.

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J Svartberg, M Midtby, KH Bonaa, J Sundsfjord, RM Joakimsen and R Jorde

OBJECTIVE: To study whether lifestyle factors and/or chronic disease are associated with the age-related decline of total and free testosterone in men, or if these factors might be associated with the variation of total and free testosterone but not with their age-related decline. DESIGN: A population-based, cross-sectional study was used. METHODS: Total testosterone and sex hormone binding globulin (SHBG) levels were analyzed and free testosterone levels were calculated in 1563 men participating in the Tromso study in 1994/1995. Anthropometric characteristics were also measured and two standardized questionnaires completed, including lifestyle factors and medical history. The data were analyzed with multiple linear regression analysis of covariance, and logistic regression. RESULTS: Total and free testosterone were inversely associated (P=0.001 and P<0.001), while SHBG was positively associated (P<0.001) with age. Body mass index (BMI) was inversely associated with total (P<0.001) and free (P=0.016) testosterone and SHBG (P<0.001). Both total and free testosterone were positively associated with tobacco consumption (P<0.001 and P=0.004) and total testosterone was positively associated with coffee consumption (P<0.001). SHBG was positively associated with smoking (P=0.004) and coffee consumption (P<0.001). Men who reported having had a stroke or having a cancer diagnosis had lower levels of total testosterone (P<0.001 and P<0.01) and free testosterone (P<0.01). CONCLUSIONS: BMI and smoking are independent contributors to the variation of total and free testosterone and SHBG levels, and coffee consumption to the variation of total testosterone and SHBG. Thus, lifestyle factors can have a direct effect on circulating levels of free endogenous sex hormones and to total levels due to the effect on SHBG levels.