Biomaterial

Serum 25-hydroxyvitamin D (25(OH)D) and parathyroid hormone (PTH)


LASAC862
LAS2B862
LASAG862

Contact: Natasja van Schoor

Background
Vitamin D deficiency is common in older western individuals. Depending on country and used definition the prevalence of vitamin D deficiency ranges from 0 up to 90% (1). 
The precursor of active vitamin D, cholecalciferol, is formed in the skin under influence of sunlight or obtained from nutrients, especially fatty fish. Cholecalciferol is hydroxylated in the liver into 25-hydroxyvitamin D3 (25(OH)D). Subsequently, the active metabolite (1,25-hydroxyvitamin D3 (1,25(OH)2D)) is formed in the kidney (2). 
Vitamin D is essential in several physiolo
gical processes, such as the mineralization of bone (2). In addition, vitamin D deficiency is found to associate with several diseases and conditions, for example diabetes mellitus, low physical performance, chronic obstructive pulmonary disease, and (osteoporotic) fractures (3-6).
Parathyroid hormone stimulates the hydroxylation of 25(OH)D into 1,25(OH)2D. A negative feedback system through calcium and directly through 1,25(OH)2D is responsible for the balance between PTH and vitamin D status (2).

Measurements in LASA

Blood collection
Blood samples for measurement of serum 25-hydroxyvitamin D (25(OH)D) and parathyroid hormone (PTH) were obtained in 1995/96 (cycle C of first LASA cohort) and 2009 (cycle G of first LASA cohort), and 2002/03 (cycle 2B of second LASA cohort) and 2009 (cycle G of second LASA cohort).

Measurement procedure & variable information
At cycle C and 2B, morning blood samples were drawn. Subjects were only allowed to take tea and toast, but no dairy products. At cycle G, fasting blood samples were drawn. Subjects were not allowed to take any food or drinks from midnight. The samples were centrifuged and stored at -20˚C until determination. Determination took place in 1997/98 for the samples from cycle C and in 2010/11 for the samples from cycles 2B and G. All analyses were performed at the Endocrine Laboratory of the VU University Medical Center.

In cycle C, blood samples were drawn from 1352 respondents. Measurements of 25(OH)D and PTH were available for 1320 individuals. In cycle 2B, blood samples were obtained from 748 individuals. Measurements were available for 739 respondents. In cycle G, blood samples were obtained from 935 respondents. Measurements of 25(OH)D were available for 917 respondents and measurements of PTH were available for 915 respondents.

For analyses on serum 25(OH)D, a competitive protein binding assay was used in 1997/98 (Nichols Diagnostics Capistrano, CA, USA) and in 2010/2011 a radioimmunoassay was used (Diasorin, Stillwater, Minesota, USA). The Nichols device used serum, whereas the Diasorin device used EDTA for the measurement of 25(OH)D. To compare both methods, cross calibration was performed by measuring 41 samples from 1995/96 at the Diasorin in 2010. Passing and Bablok regression analyses resulted in the following regression formula: Diasorin=8.0966 + 0.9218*Nichols. The correlation coefficient r=0.8765.

Serum PTH was determined by an immunoradiometric assay in 1997/98 (Incstar Corp., Stillwater, MN, USA), and by immunometric assay, Luminescence (Architect, Abbott Laboratories, Diagnostics Division, Abbott Park, Chigaco, Illinois USA) in 2010/11. Both devices used EDTA for the measurement of PTH. 


Lower limit of quantitation

Interassay coefficient of variation

1997/98

2010/11

1997/98

2010/11

25(OH)D

10 nmol/l

5 nmol/l

10%

10%

PTH

0.7 pmol/l

0.5 pmol/l

12%

5%


Descriptives

Mean serum 25(OH)D (standard deviation) (in nmol/L) and PTH (standard deviation) (in pmol/L)


LASA C

LASA 2B

LASA G

Serum 25(OH)D

PTH

53.2 (24.0)

56.5 (20.3) §

65.3 (21.8) §

3.6(2.1)

6.0 (2.5)

6.3 (2.9)

* See paragraph on outliers
§ values without outliers: 2B: 182.8 nmol/L, G: 624.4 nmol/L + 961 nmol/L
† values without outliers: C: 50.60 pmol/L, 2B: 51.76 pmol/L, G: 51.89 pmol/L

Outliers /handling the data in the analyses
In cycle G, we marked two measurements of 25(OH)D as missing values, because these values are unreliable high. In cycle 2B, one respondent’s serum 25(OH)D was 182,8 nmol/L. Although, from a statistical view this value is an outlier, it must be researcher’s own decision whether this value will be handled as missing in the analyses. In addition, in cycle 2B and G, there is one respondent with a PTH level above 50 pmol/L. These values could be explained by the respondents’ poor renal function. In cycle C, one respondent had a PTH level above 50 pmol/L. Unfortunately, we had no information on respondent’s renal function. We advise to mark all these values as missing in the analyses. When using one measurement cycle to analyze serum 25(OH)D, it is preferable to use the results of the vitamin D assay at that time point. When comparing serum 25(OH)D between different time points, the results of the Nichols assay can be converted to the Diasorin using the regression formula described in the Methods section.

Availability of data per wave

Numbers per wave

25(OH)D

 

B

C

 
2B*

G



3B*

All regions

 

1320

739

917

 

* 2B=baseline second cohort;
   3B=baseline third cohort

PTH

 

B

C


2B*

G



3B*

All regions

 

1320

739

915

 

* 2B=baseline second cohort;
   3B=baseline third cohort

Previous use in LASA
The LASA data has been used to investigated vitamin D-deficiency as independent risk factors for osteoporotic fractures. Moreover, the role of vitamin D has been assessed in relation to other indicators of physical functioning, including factors underlying fractures such as bone mineral density, as well as sarcopenia and overall physical performance, confirming that vitamin D status is implicated in much musculoskeletal morbidity in old age, and identifying threshold levels of vitamin D at which intervention is warranted. Examples of LASA articles on vitamin D:

  • Van Schoor NM, Visser M, Pluijm SMF, Kuchuk N, Smit JH, Lips P. Vitamin D deficiency as a risk factor for osteoporotic fractures. Bone 2008;42:260–66.
  • Kuchuk NO, Pluijm SM, Van Schoor NM, Looman CW, Smit JH, Lips P. Relationships of serum 25-hydroxyvitamin D to bone mineral density and serum parathyroid hormone and markers of bone turnover in older persons. J Clin Endocrinol Metab 2009;94: 1244–50.
  • Visser M, Deeg DJ, Lips P. Low vitamin D and high parathyroid hormone levels as determinants of loss of muscle strength and muscle mass (sarcopenia): the Longitudinal Aging Study Amsterdam. J Clin Endocrinol Metab 2003;88: 5766–72.
  • Wicherts IS, Van Schoor NM, Boeke AJ et al. Vitamin D status predicts physical performance and its decline in older persons. J Clin Endocrinol Metab 2007;92:2058–65.
  • Sohl, E., De Jongh, R.T., Heijboer, A.C., Swart, K.M.A., Brouwer-Brolsma, E.M., Enneman, A.W., De Groot, L.C.P.G.M., Van der Velde, N., Dhonukshe-Rutten, R.A.M., Lips, P.T.A., Van Schoor , N.M. Vitamin D status is associated with physical performance: the results of three independent cohorts. Osteoporos International 2013; 24, 187-196.
  • Sohl, E., De Jongh, R.T., Heymans, M.W., Van Schoor , N.M., Lips, P.T.A. Thresholds for Serum 25(OH)D Concentrations With Respect to Different Outcomes. The Journal of Clinical Endocrinology & Metabolism 2015; 100, 6, 2480-2488.
  • Sohl, E., De Jongh, R.T., Swart, K.M.A., Enneman, A.W., van Wijngaarden, J.P., van Dijk, S.C., Ham, A.C., van der Zwaluw, N.L., Brouwer-Brolsma, E.M., Van der Velde, N., De Groot, L.C.P.G.M., te Velde, S.J., Lips, P.T.A., Van Schoor , N.M. (2015). The association between vitamin D status and parameters for bone density and quality is modified by body mass index. Calcified Tissue International 2015; 96, 2, 113-122.
  • Van den Heuvel, E.G.H.M., Van Schoor , N.M., De Jongh, R.T., Visser, M., Lips, P.T.A. Cross-sectional study on different characteristics of physical activity as determinants of vitamin D status; inadequate in half of the population. European Journal of Clinical Nutrition 2013; 67, 360-365.

References

  1. Lips P. Vitamin D deficiency and secondary hyperparathyroidism in the elderly: consequences for bone loss and fractures and therapeutic implications. Endocr Rev. 2001;22:477-501.
  2. Lips P. Vitamin D physiology. Prog Biophys Mol Biol. 2006;92:4-8.
  3. Takiishi T, Gysemans C, Bouillon R, Mathieu C. Vitamin D and diabetes. Endocrinol Metab Clin North Am. 2010;39:419-46.
  4. Wicherts IS, van Schoor NM, Boeke AJ, Visser M, Deeg DJH, Smit J et al. Vitamin D status predicts physical performance and its decline in older persons. J Clin Endocrinol Metab. 2007;92:2058-65.
  5. Janssens W, Bouillon R, Claes B, Carremans C, Lehouck A, Buysschaert I et al. Vitamin D deficiency is highly prevalent in COPD and correlates with variants in the vitamin D-binding gene. Thorax. 2010;65:215-20.
  6. van Schoor NM, Visser M, Pluijm SMF, Kuchuk N, Smit JH, Lips P. Vitamin D deficiency as a risk factor for osteoporotic fractures. Bone. 2008;42:260-266.