Left-shifted relation between calcium and parathyroid hormone in obesity.
BACKGROUND
A condition resembling secondary hyperparathyroidism (HPT), including raised levels of PTH and normal levels of serum calcium, has been reported in obesity. A plausible reason may be vitamin D deficiency, but conflicting data have been reported.


OBJECTIVE
Our objective was to investigate calcium homeostasis in obese individuals with emphasis on the function of the parathyroid glands.


METHODS
Morbidly obese patients (mean body mass index=46.6+/-6) were examined for their status of calcium homeostasis. A subset was thoroughly investigated with calcium-citrate (CiCa) clamping.


METHODS
Of 108 morbidly obese patients, 11 underwent CiCa clamping as well as 21 healthy volunteers of normal weight and 15 with primary HPT (pHPT). Large patient cohorts of normal individuals and pHPT patients were also used as comparisons.


RESULTS
All obese individuals had normal serum calcium and creatinine levels. Mean levels of 25-OH-vitamin D3 in serum were low, 53 nmol/liter (reference range 75-250 nmol/liter). Mean intact plasma PTH was 5.1 pmol/liter (reference range 1.1-6.9 pmol/liter). There was a significant positive correlation between PTH and duration of obesity. CiCa clamping in obese subjects revealed a remarkably high sensitivity for calcium and a left-shifted relation between plasma calcium and PTH (set point) compared with the normal population. CiCa clamping in pHPT patients demonstrated a right-shifted PTH-Ca curve.


CONCLUSIONS
Although vitamin D levels in the obese individuals were low, few displayed overt signs of secondary HPT. The CiCa clamping implied a disturbance in the calcium homeostasis comparable to early renal insufficiency, with a left-shifted Ca-PTH curve and a lower set point compared with the normal population.
Department of Surgery, University Hospital, SE-751 85 Uppsala, Sweden. per.hellman@surgsci.uu.se.
Hella
H
Hultin
Katarina
K
Edfeldt
Magnus
M
Sundbom
Per
P
Hellman
D000328:Adult; D002118:Calcium / Q000097:blood*; D003404:Creatinine / Q000097:blood; D005260:Female; D006706:Homeostasis; D006801:Humans; D006962:Hyperparathyroidism, Secondary / Q000097:blood* / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D009767:Obesity, Morbid / Q000097:blood* / Q000503:physiopathology; D010280:Parathyroid Glands / Q000503:physiopathology*; D010281:Parathyroid Hormone / Q000097:blood*; D014808:Vitamin D Deficiency / Q000097:blood / Q000503:physiopathology
D010281:Parathyroid Hormone; D003404:Creatinine; D002118:Calcium