Abstract
Little is known about whether markers of vitamin D metabolism are associated with the development of abdominal aortic aneurysms (AAA), though these markers have been linked to other cardiovascular diseases. We tested the hypotheses that risk of AAA is higher among individuals with low serum concentrations of 25-hydroxyvitamin D [25(OH)D], and among those with elevated concentrations of calcium, fibroblast growth factor 23 (FGF23), phosphorus, and parathyroid hormone (PTH) using data from a cohort of blacks and whites with long-term follow-up. Markers of vitamin D metabolism were measured using serum collected in 1990–1992 from ARIC study participants (mean ± SD age 56.9 ± 5.7 years; 43.2% male, 23.9% black). A total of 12,770 participants were followed until 2011 for incident AAA. Multivariable-adjusted Cox regression models were used. A total of 449 incident AAA events occurred over a median follow-up of 19.7 years. For the association between serum calcium and risk of incident AAA there was evidence of interaction by sex (p-interaction 0.02). Among women, in the fully adjusted model the HR (95% CI) comparing highest to lowest quartile was 2.43 (1.25–4.73), whereas in men the HR (95% CI) was 1.01 (0.72–1.43). 25(OH)D, FGF23, phosphorus and PTH were not associated with risk of incident AAA. In this large prospective cohort, there was little evidence that markers of vitamin D metabolism are associated with risk of incident AAA. The positive association of calcium with AAA among women may warrant further investigation and replication in other populations.
Keywords: Vitamin D, Calcium, Fibroblast Growth Factor 23, Abdominal Aortic Aneurysm (AAA), Epidemiology, Atherosclerosis Risk in Communities (ARIC) Study
Introduction
Abdominal aortic aneurysm (AAA) is a condition in which a portion of the aortic wall undergoes progressive dilation and weakening, potentially leading to aortic rupture if untreated.1 In the United States in 2014 aortic aneurysm (of which most are abdominal) was listed as the primary cause of 9,863 deaths and a contributing cause in than 16,242 deaths.2
Key features thought to underlie the pathogenesis of AAA are the progressive degradation and remodeling of elastin and collagen fibers in the aortic wall.3,4 Relatively little is known about the etiology of AAA, though age, male sex, smoking status and hypertension are important risk factors. Serum concentrations of 25-hydroxyvitamin D (vitamin D, 25(OH)D), calcium, parathyroid hormone (PTH), fibroblast growth factor 23 (FGF23) and phosphorus – all biomarkers in the vitamin D metabolic pathway – may potentially contribute to AAA development. Briefly, suboptimal 25(OH)D, PTH and calcium concentrations have been linked to several AAA risk factors such as hypertension,5–11 inflammation12,13 and vascular calcification.14,15 Elevated FGF23 has been related to aneurysmal development in both in vitro studies of human and rat aorta cells16 and in rat experimental models.17 High phosphate concentrations precede elevated FGF23 and have been associated with vascular calcification18–20 and myocardial fibrosis.21
To date, no prospective epidemiologic studies have examined the association between serum markers of vitamin D metabolism and incidence of AAA. Using data from the population-based Atherosclerosis Risk in Communities (ARIC) cohort we tested the hypotheses that risk of AAA is higher among individuals with low concentration of 25(OH)D and among those with elevated concentrations of calcium, FGF23, phosphorus and PTH, over long-term follow-up.
Methods
Study design and population
The ARIC study22 is a population-based prospective cohort which in 1987–1989 enrolled 15,792 men and women, aged 45–64, from 4 U.S. field centers: suburban Minneapolis, Minnesota; Forysth County, North Carolina; Washington County, Maryland; Jackson, Mississippi. Participants have taken part in several clinic visits, and have been followed continuously for health outcomes. Relevant to the present analysis, serum from visit 2 (1990–1992) was used for the measurement of markers of vitamin D metabolism. At each clinic visit participants provided informed consent. The ARIC study protocol was approved by Institutional Review Boards at all study centers.
Of the original 15,792 participants, 14,348 attended visit 2, which is baseline for the present analysis. We excluded participants with a) baseline definite or probable AAA (n = 46), b) race other than black or white (n = 42) and blacks at the Minnesota and Maryland centers (n = 50) due to small numbers, as well as those who were c) missing any biomarkers of interest (n = 1,437) or d) had no follow-up after visit 2 (n = 3). The final analytic sample was 12,770.
Biomarker measurement
Participants were asked to fast for 12 hours prior to the visit 2 blood draw. Serum was frozen at −70°C until analyzed in 2012–2013. Serum 25(OH)D2 and 25(OH)D3 were measured using a high sensitivity mass spectrometer (AB Sciex 5500) at the University of Minnesota Molecular Epidemiology and Biomarker Research Laboratory, which for vitamin D is traceable to the U.S. Centers for Disease Control reference measurement procedures.23 Using samples split at the time of blood draw and sent to the lab 1 week apart, the blind duplicate coefficient of variation (CV) and Pearson correlation coefficients were as follows: 25(OH)D3 CV = 6.9%, r = 0.97; 25(OH)D2 CV = 20.8%, r = 0.98. Please note that these estimates encompass variability occurring as a consequence of sample processing, shipping, long-term storage and laboratory analysis. Serum calcium and phosphorus were measured on a Roche Modular P800 Chemistry Analyzer (Roche Diagnostics, Indianapolis, IN) using a colorimetric method. Using the ARIC blind duplicates, the CVs were 2.4% and 3.0%, respectively. Serum parathyroid hormone was measured on a Roche Elecsys 2010 analyzer using a sandwich immunoassay method (Roche Diagnostics) (CV = 9.7%). Serum FGF23 was measured with a two site enzyme-linked immunosorbent assay (Kainos Laboratories, Inc., Tokyo, Japan). The CV for FGF23 based on ARIC blind duplicate samples was 16.6%, while the CV from internal laboratory QC samples was 8.8% at 41.4 pg/mL.
Outcome ascertainment
Incident AAA events accrued from baseline through the 2011. Since baseline, ARIC study participants have been followed continuously for hospitalizations and deaths, through annual or semi-annual telephone calls to ARIC participants (or proxy), active surveillance of hospital discharge lists, and linkage to state and national death records. Additionally, for the period from 1991–2011 we linked participant identifiers with Medicare data from the Centers for Medicare and Medicaid Services (CMS), to find any missing hospital or outpatient AAA events for those over 65 years. Clinical AAAs were defined as those who had a hospital discharge diagnosis from any of the above sources, or two Medicare outpatient claims that occurred at least one week apart, with ICD-9-CM codes of 441.3 (ruptured AAA), 441.4 (AAA without mention of rupture) or 441.02 (AAA dissection), or procedure codes of 38.44 (AAA resection and replacement) or 39.71 (AAA endovascular repair), or a listed cause of death coded as ICD-9 441.3 or 441.4 or ICD-10 code I71.02 (AAA dissection), I71.3 (ruptured AAA), or I71.4 (AAA without mention of rupture).24 Notably, some of these clinical diagnoses would include asymptomatic AAAs that were captured through imaging for other indications.
Covariate information
Information on covariates was collected at the visit 2 clinic visit. Age, race, field center, sex, and smoking status and amount were self-reported. Pack-years were calculated. Participants brought to the visit all medications taken in the 2 weeks before the examination; medication names were transcribed and coded. Height, weight and blood pressure were measured. Diabetes was defined by fasting blood glucose ≥126 mg/dL, nonfasting glucose ≥200 mg/dL, a self-report of physician diagnosis, or current medication use for diabetes. Plasma total cholesterol, triglycerides, and high-density lipoprotein cholesterol (HDL-C) were measured using standard ARIC procedures.25 Estimated glomerular filtration rate (eGFR) was calculated using the 2012 CKD EPI equation, which incorporates both cystatin C and creatinine.26 eGFR was categorized according to established clinical cut-points: ≥90, 60–89 and ≤59 mL/min/1.73 m2.
Data analysis
Serum 25(OH)D was the sum of 25(OH)D2 and 25(OH)D3. Concentrations were corrected to account for seasonality using a residuals approach.27 Approximately 40% of non-skeletal calcium is bound to proteins, primarily albumin and globulin.28 As such, serum calcium was corrected for serum albumin with the use of the following equation: measured total calcium (mg/dL) + 0.8 [4.0 − serum albumin (g/dL)].29 Albumin-corrected calcium was used for all analyses. Participant characteristics are presented as means and proportions, stratified by 25(OH)D commonly used clinical cut-points30,31 and serum calcium quartiles, respectively.
Cox proportional hazards models were used to calculate hazards ratios (HRs) and 95% confidence intervals (CIs) of the association between markers of vitamin D metabolism and incident AAA. Person time accrued from the date of the visit 2 clinic visit until AAA diagnosis, death, loss-to-follow-up or December 31, 2011; whichever came first. Model 1 adjusted for age, sex and race. Model 2 additionally adjusted for height, weight, smoking status (current, former, never) and lifetime smoking quantity [ln(pack years + 1)]. Model 3 further adjusted for total cholesterol, HDL cholesterol, systolic blood pressure, diabetes, antihyperlipidemic medication, antihypertensive medication, and eGFR categories. Models where PTH was the biomarker of interest also adjusted for season, with a 1-month lag: July-September, October-December, January-March, April-June. Linear trends were calculated by including the exposure categories in the models as an ordinal term.
Multiplicative interactions were tested by age, race, sex, smoking status and eGFR (for FGF23 only). Subgroup analyses are reported, as appropriate. There were no meaningful violations of the proportional hazards assumption. SAS version 9.3 (SAS Institute, Inc., Cary, NC) was used for all analyses.
Results
At baseline, participants were 43.2% male, 23.9% black, and on average (±SD) 56.9 ± 5.7 years old. The mean (±SD) concentrations of the vitamin D metabolism biomarkers are as follows: 25(OH)D = 24.4 ± 8.5 ng/mL, corrected calcium 9.21 ± 0.41 mg/dL, phosphorus = 3.53 ± 0.48 mg/dL, PTH = 42.1 ± 16.5 pg/mL). FGF23 was highly skewed; the median (25th, 75th percentiles) was 41.9 (33.9–51.7) pg/mL. Table 1 presents participant baseline characteristics stratified by 25(OH)D categories, and Table 2 by calcium quartiles. As expected, blacks had lower 25(OH)D concentrations than did whites. In general, individuals with lower 25(OH)D and higher serum calcium had worse cardiometabolic profiles.
Table 1.
Baseline characteristics by 25(OH)D clinical cutpoints: the Atherosclerosis Risk in Communities study 1990-92, (N=12,770)a
| Serum 25(OH)D, ng/mL | ≥30 | 20 to <30 | 10 to <20 | <10 |
|---|---|---|---|---|
| Median | 34.3 | 24.8 | 16.3 | 8.6 |
| N | 2966 | 5706 | 3765 | 333 |
| Age, y | 57.4±5.7 | 57.0±5.7 | 56.4±5.7 | 55.5±5.7 |
| Male, n (%) | 1514 (51.1) | 2728 (47.8) | 1198 (31.8) | 75 (22.5) |
| Race, n (%) | ||||
| White | 2779 (93.7) | 4708 (82.5) | 2095 (55.6) | 138 (41.4) |
| Black | 187 (6.3) | 998 (17.5) | 1670 (44.4) | 195 (58.6) |
| Smoking status, n (%) | ||||
| Current | 571 (19.3) | 1145 (20.1) | 966 (25.7) | 102 (30.6) |
| Former | 1308 (44.1) | 2195 (38.5) | 1207 (32.1) | 91 (27.3) |
| Never | 1087 (36.7) | 2366 (41.5) | 1592 (42.3) | 140 (42.0) |
| Smoking, pack-years | 26.4±39.9 | 26.1±41.6 | 26.8±41.9 | 32.7±49.9 |
| Height, cm | 169.3±9.4 | 169.0±9.3 | 166.7±9.0 | 165.9±8.5 |
| Weight, lb | 166.2±32.7 | 175.3±36.0 | 180.1±40.1 | 179.1±46.8 |
| Diabetes, n (%) | 258 (8.7) | 771 (13.5) | 748 (20.0) | 69 (20.8) |
| SBP, mmHg | 119.0±17.7 | 120.7±18.4 | 123.7±19.6 | 125.4±20.8 |
| Total cholesterol, mg/dL | 209.4±37.7 | 210.0±38.7 | 210.3±41.0 | 210.7±43.3 |
| HDL-C, mg/dL | 51.4±17.9 | 48.7±16.1 | 50.0±16.8 | 52.0±18.0 |
| eGFR, mL/min/1.73m2 | 93.0±15.8 | 95.1±16.0 | 97.2±18.0 | 98.2±20.3 |
| eGFR categories | ||||
| >90 mL/min/1.73m2 | 1805 (60.9) | 3728 (65.3) | 2607 (69.2) | 233 (70.0) |
| 60-90 mL/min/1.73m2 | 1072 (36.1) | 1842 (32.3) | 1050 (27.9) | 89 (26.7) |
| <60 mL/min/1.73m2 | 89 (3.0) | 136 (2.4) | 108 (2.9) | 11 (3.3) |
| BP medication, n (%) | 606 (20.5) | 1467 (25.8) | 1204 (32.2) | 106 (32.0) |
| Lipid medication, n (%) | 214 (7.2) | 378 (6.6) | 199 (5.3) | 16 (4.8) |
| PTH, pg/mL | 36.8±12.6 | 40.8±14.5 | 47.0±18.9 | 55.0±25.4 |
| FGF23, pg/mL | 46.7±80.5 | 45.8±104.1 | 45.5±115.9 | 42.7±18.4 |
| Calcium, mg/dLb | 9.2±0.4 | 9.2±0.4 | 9.3±0.4 | 9.3±0.5 |
| Phosphorus, mg/dL | 3.5±0.5 | 3.5±0.5 | 3.6±0.5 | 3.6±0.5 |
Mean±SD, unless otherwise noted.
Corrected for serum albumin concentrations.
25(OH)D, 25-hydroxyvitamin D; SBP, systolic blood pressure; HDL-C, high density lipoprotein cholesterol; eGFR, estimated glomerular filtration rate; BP medication, blood pressure medication; PTH, parathyroid hormone; FGF23, fibroblast growth factor 23.
Table 2.
Baseline characteristics by serum calciuma concentrations quartiles: the Atherosclerosis Risk in Communities study 1990-92, (N=12,770)b
| Serum Calcium, mg/dLa | Q1 | Q2 | Q3 | Q4 |
|---|---|---|---|---|
| Median | 8.8 | 9.1 | 9.3 | 9.6 |
| Range | 3.3-8.9 | 80-.9-9.2 | 9.2-9.4 | 9.5-11.8 |
| N | 3192 | 3211 | 3183 | 3184 |
| Age, y | 56.3±5.7 | 56.6±5.8 | 57.0±5.7 | 57.5±5.6 |
| Male, n (%) | 1781 (55.8) | 1511 (47.1) | 1253 (39.4) | 970 (30.5) |
| Race, n (%) | ||||
| White | 2807 (87.9) | 2625 (81.8) | 2362 (74.2) | 1926 (60.49) |
| Black | 385 (12.1) | 586 (18.3) | 821 (25.8) | 1258 (39.5) |
| Smoking status, n (%) | ||||
| Current | 596 (18.7) | 666 (20.7) | 736 (23.1) | 786 (24.7) |
| Former | 1329 (41.6) | 1302 (40.6) | 1125 (35.3) | 1045 (32.8) |
| Never | 1267 (39.7) | 1243 (38.7) | 1322 (41.5) | 1353 (42.5) |
| Smoking, pack-years | 26.6±42.5 | 26.1±40.6 | 27.2±42.3 | 26.3±40.6 |
| Height, cm | 170.4±9.4 | 169.1±9.3 | 167.5±9.1 | 166.3±8.8 |
| Weight, lb | 174.9±36.3 | 174.6±36.6 | 173.4±36.4 | 175.7±39.5 |
| Diabetes, n (%) | 338 (10.6) | 377 (11.8) | 468 (14.7) | 663 (20.9) |
| SBP, mmHg | 119.6±17.6 | 120.5±18.6 | 121.6±19.0 | 123.6±19.5 |
| Total cholesterol, mg/dL | 203.5±38.8 | 208.5±37.4 | 211.3±38.2 | 216.6±41.6 |
| HDL-C, mg/dL | 47.8±16.6 | 49.3±16.5 | 50.8±17.1 | 51.4±16.8 |
| eGFR, mL/min/1.73m2 | 97.9±14.8 | 96.3±16.0 | 95.1±16.5 | 91.8±19.0 |
| eGFR categories | ||||
| >90 mL/min/1.73m2 | 2294 (71.9) | 2200 (68.5) | 2057 (64.6) | 1822 (57.2) |
| 60-90 mL/min/1.73m2 | 869 (27.2) | 944 (29.4) | 1050 (33.0) | 1190 (37.4) |
| <60 mL/min/1.73m2 | 29 (0.9) | 67 (2.1) | 76 (2.4) | 172 (5.4) |
| BP medication, n(%) | 586 (18.4) | 719 (22.5) | 858 (27.1) | 1220 (38.5) |
| Lipid medication, n(%) | 184 (5.8) | 192 (6.0) | 209 (6.6) | 222 (7.0) |
| PTH, pg/mL | 42.8±15.5 | 41.7±15.0 | 41.3±15.7 | 42.4±19.3 |
| FGF23, pg/mL | 42.3±14.7 | 43.3±15.1 | 44.1±15.9 | 53.8±201.5 |
| 25(OH)D, ng/mL | 25.1±8.5 | 24.8±8.4 | 24.3±8.4 | 23.2±8.5 |
| Phosphorus, mg/dL | 3.4±0.5 | 3.5±0.5 | 3.6±0.5 | 3.7±0.5 |
Corrected for serum albumin concentrations.
Mean±SD, unless otherwise noted.
25(OH)D, 25-hydroxyvitamin D; SBP, systolic blood pressure; HDL-C, high density lipoprotein cholesterol; eGFR, estimated glomerular filtration rate; BP medication, blood pressure medication; PTH, parathyroid hormone; FGF23, fibroblast growth factor 23.
Over a median follow-up of 19.7 years (maximum 21.9 years) a total of 449 incident AAA events occurred. As shown in Table 3, 25(OH)D concentrations were not associated with risk of AAA. The HR (95% CI) for 25(OH)D concentrations <10 ng/mL vs. ≥30 ng/mL was 1.63 (0.82–3.23) after accounting for demographics (model 1),1.21 (0.59–2.50) after further adjusting for indices of anthropometry and smoking (model 2), and 1.10 (0.51–2.38) after additionally adjusting for cholesterols, blood pressure, diabetes and eGFR (model 3). Findings were similar in analyses stratified by race. There was no evidence of interaction by age, race, sex, or smoking status (interaction p-values all >0.18).
Table 3.
Incidence ratesa and adjusted hazard ratiosb (95% CIs) of incident AAA by vitamin D metabolism biomarkers: The Atherosclerosis Risk in Communities Study, 1990-2011 (N=12,770)
| 25(OH)D | P for trend | ||||
| Category, ng/mL | ≥30 | 20-<30 | 10-<20 | <10 | |
| # Events/Total | 133/2966 | 192/5706 | 115/3765 | 9/270 | |
| Incidence Ratea | 2.50 | 1.89 | 1.76 | 1.67 | |
| Model 1 | 1 (ref) | 0.87 (0.69-1.08) | 1.21 (0.93-1.57) | 1.63 (0.82-3.23) | 0.13 |
| Model 2 | 1 (ref) | 0.85 (0.67-1.07) | 1.02 (0.77-1.35) | 1.21 (0.59-2.50) | 0.83 |
| Model 3 | 1 (ref) | 0.84 (0.66-1.06) | 1.00 (0.76-1.33) | 1.10 (0.51-2.38) | 0.99 |
| Calciumb | Quartile 1 | Quartile 2 | Quartile 3 | Quartile 4 | |
| Median, mg/dL | 8.78 | 9.08 | 9.32 | 9.65 | |
| # Events/Total | 120/3192 | 102/3211 | 108/3183 | 119/3184 | |
| Incidence Ratea | 2.09 | 1.78 | 1.89 | 2.20 | |
| Model 1 | 1 (ref) | 0.95 (0.73-1.24) | 1.13 (0.87-1.46) | 1.63 (1.25-2.12) | 0.0003 |
| Model 2 | 1 (ref) | 0.90 (0.68-1. 18) | 1.01 (0.77-1.32) | 1.39 (1.05-1.83) | 0.02 |
| Model 3 | 1 (ref) | 0.85 (0.64-1.12) | 0.94 (0.72-1.23) | 1.19 (0.90-1.58) | 0.23 |
| PTH | Quartile 1 | Quartile 2 | Quartile 3 | Quartile 4 | |
| Median, pg/mL | 26.24 | 35.04 | 43.70 | 58.80 | |
| # Events/Total | 151/3195 | 113/3190 | 105/3197 | 80/3188 | |
| Incidence Ratea | 2.71 | 1.97 | 1.85 | 1.43 | |
| Model 1 | 1 (ref) | 0.71 (0.55-0.90) | 0.69 (0.54-0.89) | 0.57 (0.44-0.76) | <0.0001 |
| Model 2 | 1 (ref) | 0.87 (0.67-1.12) | 0.88 (0.67-1.15) | 0.79 (0.58-1.07) | 0.14 |
| Model 3 | 1 (ref) | 0.89 (0.69-1.15) | 0.90 (0.69-1.17) | 0.76 (0.56-1.04) | 0.10 |
| FGF23 | Quartile 1 | Quartile 2 | Quartile 3 | Quartile 4 | |
| Median, pg/mL | 28.77 | 37.93 | 46.32 | 60.79 | |
| # Events/Total | 100/3192 | 115/3193 | 116/3193 | 118/3192 | |
| Incidence Ratea | 1.75 | 2.01 | 2.05 | 2.16 | |
| Model 1 | 1 (ref) | 1.09 (0.83-1.43) | 1.06 (0.81-1.38) | 1.13 (0.87-1.48) | 0.43 |
| Model 2 | 1 (ref) | 1.24 (0.94-1.65) | 1.17 (0.88-1.54) | 1.28 (0.96-1.70) | 0.14 |
| Model 3 | 1 (ref) | 1.14 (0.86-1.51) | 1.01 (0.76-1.34) | 1.00 (0.75-1.34) | 0.78 |
| Phosphorus | Quartile 1 | Quartile 2 | Quartile 3 | Quartile 4 | |
| Median, mg/dL | 3.0 | 3.4 | 3.7 | 4.2 | |
| # events/total | 178/3656 | 99/2991 | 105/3738 | 67/2385 | |
| Incidence Ratea | 2.79 | 1.87 | 1.58 | 1.58 | |
| Model 1 | 1 (ref) | 0.80 (0.63-1.03) | 0.84 (0.66-1.08) | 1.07 (0.79-1.44) | 0.79 |
| Model 2 | 1 (ref) | 0.83 (0.64-1.08) | 0.77 (0.60-1.01) | 0.81 (0.59-1.12) | 0.08 |
| Model 3 | 1 (ref) | 0.83 (0.64-1.07) | 0.82 (0.63-1.07) | 0.86 (0.62-1.18) | 0.20 |
Abbreviations: AAA = abdominal aortic aneurysm; CI = confidence interval; 25(OH)D = 25-hydroxyvitmain D; PTH = parathyroid hormone; FGF23 = fibroblast growth factor 23
Unadjusted incidence rate per 1000 person-years.
Model 1 was adjusted for age, sex, race. PTH was also adjusted for season of blood draw.
Model 2 was adjusted for model 1 + height, weight, smoking status and smoking amount [ln(pack-years + 1)]
Model 3 was adjusted for model 2 + total cholesterol, high density lipoprotein cholesterol , systolic blood pressure, diabetes, cholesterol and blood pressure medication, estimated glomerular filtration rate (categories).
Corrected for serum albumin concentrations.
For serum calcium, participants in the highest versus lowest quartile were at higher risk of incident AAA after Model 1 adjustments [HR=1.63 (1.25–2.12)], but this association was attenuated with additional adjustment for anthropometrics and smoking [1.39 (1.05–1.83)] and became nonsignificant after adjustment for traditional cardiovascular risk factors [1.19 (0.90–1.58)]. There was evidence of interaction by sex (p for interaction in model 1 = 0.02; model 2 = 0.02; model 3 = 0.02), whereby the association appeared stronger in women than in men (Table 4). In the fully adjusted models, the women in the highest quartile of serum calcium (versus the lowest) had a HR for incident AAA of 2.43 (1.25–4.73), while in men the HR was 1.01 (0.72–1.43). Results were similar when sex-specific serum calcium quartiles were utilized (data not shown). There were no statistically significant interactions by age, race or smoking status.
Table 4.
Sex-stratified adjusted incidence ratesa and adjusted hazard ratiosb (95% CIs) of AAA by serum calcium quartiles: The Atherosclerosis Risk in Communities Study, 1990-2011 (N=12,770)
| Serum Calciumc | |||||
|---|---|---|---|---|---|
| Median, mg/dL | Quartile 1 | Quartile 2 | Quartile 3 | Quartile 4 | P for trend |
| Women | |||||
| Median, mg/dL | 8.79 | 9.09 | 9.32 | 9.66 | |
| # Events/Total | 11/1411 | 32/1700 | 32/1930 | 59/2214 | |
| Incidence Ratea | 0.42 | 1.02 | 0.90 | 1.51 | |
| Model 1 | 1 (ref) | 2.33 (1.17-4.63) | 2.02 (1.02-4.02) | 3.50 (1.82-6.71) | 0.0002 |
| Model 2 | 1 (ref) | 2.20 (1.10-4.41) | 1.73 (0.86-3.48) | 2.80 (1.44-5.42) | 0.006 |
| Model 3 | 1 (ref) | 2.21 (1.10-4.43) | 1.62 (0.80-3.27) | 2.43 (1.25-4.73) | 0.03 |
| Men | |||||
| Median, mg/dL | 8.79 | 9.08 | 9.31 | 9.63 | |
| # Events/Total | 109/1781 | 70/1511 | 766/1253 | 60/970 | |
| Incidence Ratea | 3.51 | 2.69 | 3.55 | 4.04 | |
| Model 1 | 1 (ref) | 0.79 (0.59-1.07) | 1.06 (0.79-1.43) | 1.35 (0.98-1.86) | 0.07 |
| Model 2 | 1 (ref) | 0.74 (0.54-1.01) | 0.97 (0.72-1.32) | 1.19 (0.85-1.66) | 0.33 |
| Model 3 | 1 (ref) | 0.69 (0.50-0.95) | 0.90 (0.66-1.22) | 1.01 (0.72-1.43) | 0.90 |
Abbreviations: AAA = abdominal aortic aneurysm; CI = confidence interval
Unadjusted incidence rate per 1000 person-years.
Model 1 was adjusted for age, race.
Model 2 was adjusted for model 1 + height, weight, smoking status and smoking amount [ln(pack-years + 1)]
Model 3 was adjusted for model 2 + total cholesterol, high density lipoprotein cholesterol, systolic blood pressure, diabetes, cholesterol and blood pressure medications, estimated glomerular filtration rate (categories).
Corrected for serum albumin concentrations.
Neither FGF23 nor phosphorus was associated with risk of incident AAA in any of the models explored (Table 3). The demographic-adjusted (model 1) HR for the highest versus lowest quartiles of FGF23 and phosphorus were 1.13 (0.87–1.48) and 1.07 (0.79–1.44), respectively. For PTH, participants in the highest versus lowest quartile were at lower risk of incident AAA [0.57 (0.44–0.76)], after model 1 adjustments. However, this HR was attenuated with Model 2 adjustments [0.79 (0.58–1.07)]. There was no evidence of interaction by age, race, sex, or smoking status (interaction p-values all >0.12).
Discussion
In this large population-based prospective cohort there was little evidence that markers of vitamin D metabolism are associated with risk of incident AAA. For serum calcium a statistically significant interaction by sex was observed. In analyses restricted to women, high versus low serum calcium was associated with an approximately doubling of AAA risk, even after accounting for traditional cardiovascular risk factors. There was no association between serum calcium and AAA risk in men. Other markers of vitamin D metabolism, namely 25(OH)D, FGF23, phosphorus and PTH were not associated with risk of AAA. These finding provide the first prospective assessment of markers of vitamin D metabolism and future AAA risk in humans.
If suboptimal 25(OH)D or elevated serum calcium or PTH influence AAA risk, they likely do so by elevating established cardiovascular risk factors, namely hypertension,5–11 inflammation12,13 and vascular calcification.14,15 Our analysis did not provide convincing evidence that either 25(OH)D or PTH [which is downstream from 25(OH)D], are associated with AAA development. This is in contrast to the existing, albeit limited, literature. Evidence from animal models support the hypothesis that 25(OH)D may be associated with AAA risk. Specifically, it was recently reported that in an apolipoprotein E-knockout mouse model, treatment with calcitriol reduced dissecting AAA formation.32 In humans, a cross-sectional study which screened older men for AAA reported a dose-response relationship between low 25(OH)D concentrations and greater abdominal aortic diameter.33 Cross-sectional associations involving 25(OH)D should be viewed with caution, as reverse causation may occur since individuals with poorer health states often get less sunlight exposure and consequently have lower 25(OH)D concentrations. Higher PTH has been associated with impaired endothelial function, increased aortic pulse pressure, and decreased large artery elasticity.34
Among ARIC participants, serum calcium was positively associated with incident AAA in women, but not in men. The potential role of calcium in cardiovascular disease, and more specifically in vascular calcification, is both controversial and complex.14,35–37 Emerging evidence suggests that initiation of calcification within the vasculature may be carefully regulated by osteoclast-like and osteoblast-like cells, in a process similar to that observed in bone.36 Intake of calcium, in the form of dietary supplements, may transiently elevate serum calcium and by doing so disrupt homeostasis and promote vascular calcification.14,35 Our finding that serum calcium is associated with greater risk of AAA in women should be viewed as hypothesis generating and requires independent confirmation, as this sex interaction was unanticipated and may be due to chance. It is, however, notable that women take more dietary supplements than do men,38 and among women taking calcium supplements 9% had evidence of hypercalcemia and 31% had hypercalcuria.39 Whether calcium supplement intake may be leading to calcification of the abdominal aorta is unknown.
In the present analysis we found no evidence that serum FGF23 or phosphorus were linked to AAA risk. This is counter to intriguing mechanistic evidence, which prompted us to test these hypotheses. Although much interest in FGF23 has related to its potential role in left ventricular hypertrophy,40 the co-receptor Klotho, which is mandatory to induce FGF23 signaling pathways,16 is not expressed in the myocardium. It is, however, expressed in both human and rat aortas, as has been reviewed recently.16 Additionally, in a rat experimental model of AAA, relative to controls those exposed to a FGF23 antagonist had smaller aortic diameters and experienced a preservation of elastic fibers and smooth muscle cells.17 FGF23 has also been associated with hypertension,41 endothelial dysfunction42–44 and inflammation.45,46 Phosphate excess, which is upstream to high FGF23, has been associated with vascular calcification18–20 and myocardial fibrosis.21
The key strength of this study is its prospective assessment of AAA risk. Relatively few prospective studies have a sufficient number of AAA events to evaluate incidence. Additional strengths are the ascertainment of biomarkers using state-of-the-art assay methods, and the ARIC study’s extensive covariate information and active event surveillance. The key limitation of this study is that some AAA events were likely missed, perhaps particularly if the AAA event resulted in sudden death. ARIC did not conduct serial AAA screenings therefore included in this analysis are only AAA recognized clinically, either due to the indication of AAA or being captured through imaging for another indication.24 Misclassification of AAA case status would, however, likely be nondifferential, and would therefore most likely bias results toward the null. Additionally, the biomarkers were only measured once, possibly not at the right time in the natural history of AAA. Lastly, at present it is unclear which biomarker is optimal for ascertaining vitamin D status.47
Conclusion
In conclusion, despite evidence from in vitro animal and cross-sectional human studies suggesting a relation between vitamin D metabolism and the development of AAA, within the context of the prospective ARIC cohort markers of vitamin D metabolism were not substantially associated with AAA risk. The finding of greater AAA risk among women with high serum calcium concentrations requires verification in an independent cohort. AAA is an understudied cause of mortality; identifying factors which may be useful for the prevention of AAA, or for AAA screening, remains a priority.
Acknowledgements
The authors thank the staff and participants of the ARIC Study for their important contributions.
Funding
The National Institutes of Health (NIH) National Heart, Lung, and Blood Institute supported this research through R01 HL103695, R01 HL103706, and ARIC contracts HHSN268201100005C, HHSN268201100006C, HHSN268201100007C, HHSN268201100008C, HHSN268201100009C, HHSN268201100010C, HHSN268201100011C, and HHSN268201100012C. The NIH Office of Dietary Supplements also provided support through R01 HL103706-S1.
Footnotes
Disclosures
None.
References
- 1.Sakalihasan N, Limet R, Defawe OD. Abdominal aortic aneurysm. Lancet. 2005;365(9470):1577–1589. [DOI] [PubMed] [Google Scholar]
- 2.Benjamin EJ, Blaha MJ, Chiuve SE, et al. American Heart Association Statistics C, Stroke Statistics S. Heart Disease and Stroke Statistics-2017 Update: A Report From the American Heart Association. Circulation. 2017; 135: e146–e603. 10.1161/CIR.0000000000000485. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3.Thompson RW, Curci JA, Ennis TL, Mao D, Pagano MB, Pham CT. Pathophysiology of abdominal aortic aneurysms: insights from the elastase-induced model in mice with different genetic backgrounds. Ann N Y Acad Sci. 2006;1085:59–73. [DOI] [PubMed] [Google Scholar]
- 4.Thompson RW, Geraghty PJ, Lee JK. Abdominal aortic aneurysms: basic mechanisms and clinical implications. Curr Probl Surg. 2002;39(2):110–230. [DOI] [PubMed] [Google Scholar]
- 5.Forman JP, Giovannucci E, Holmes MD, et al. Plasma 25-hydroxyvitamin D levels and risk of incident hypertension. Hypertension. 2007;49(5):1063–1069. [DOI] [PubMed] [Google Scholar]
- 6.Forman JP, Curhan GC, Taylor EN. Plasma 25-hydroxyvitamin D levels and risk of incident hypertension among young women. Hypertension. 2008;52(5):828–832. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 7.Krause R, Buhring M, Hopfenmuller W, Holick MF, Sharma AM. Ultraviolet B and blood pressure. Lancet. 1998;352(9129):709–710. [DOI] [PubMed] [Google Scholar]
- 8.Pfeifer M. Effects of a Short-Term Vitamin D3 and Calcium Supplementation on Blood Pressure and Parathyroid Hormone Levels in Elderly Women. Journal of Clinical Endocrinology & Metabolism. 2001;86(4):1633–1637. [DOI] [PubMed] [Google Scholar]
- 9.Witham MD, Dove FJ, Dryburgh M, Sugden JA, Morris AD, Struthers AD. The effect of different doses of vitamin D(3) on markers of vascular health in patients with type 2 diabetes: a randomised controlled trial. Diabetologia. 2010;53(10):2112–2119. [DOI] [PubMed] [Google Scholar]
- 10.Sugden JA, Davies JI, Witham MD, Morris AD, Struthers AD. Vitamin D improves endothelial function in patients with Type 2 diabetes mellitus and low vitamin D levels. Diabet Med. 2008;25(3):320–325. [DOI] [PubMed] [Google Scholar]
- 11.Judd SE, Raiser SN, Kumari M, Tangpricha V. 1,25-dihydroxyvitamin D3 reduces systolic blood pressure in hypertensive adults: a pilot feasibility study. J Steroid Biochem Mol Biol. 2010;121(1–2):445–447. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 12.Folsom AR, Roetker NS, Rosamond WD, et al. Serum 25-hydroxyvitamin D and risk of venous thromboembolism: the Atherosclerosis Risk in Communities (ARIC) Study. J Thromb Haemost. 2014;12(9):1455–1460. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 13.Yin K, Agrawal DK. Vitamin D and inflammatory diseases. J Inflamm Res. 2014;7:69–87. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 14.Spence LA, Weaver CM. Calcium intake, vascular calcification, and vascular disease. Nutr Rev. 2013;71(1):15–22. [DOI] [PubMed] [Google Scholar]
- 15.Chin K, Appel LJ, Michos ED. Vitamin D, Calcium, and Cardiovascular Disease: A”D”vantageous or “D”etrimental? An Era of Uncertainty. Curr Atheroscler Rep. 2017;19(1):5. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 16.Jimbo R, Shimosawa T. Cardiovascular Risk Factors and Chronic Kidney Disease-FGF23: A Key Molecule in the Cardiovascular Disease. Int J Hypertens. 2014;2014:381082. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 17.Miyama N, Sato A, Matsubara M, Watanabe T, Ikada Y, Satomi S. Inhibitory effects of a biodegradable gelatin hydrogel sponge sheet on the progression of experimental abdominal aortic aneurysms. Ann Vasc Surg. 2009;23(2):224–230. [DOI] [PubMed] [Google Scholar]
- 18.Foley RN, Collins AJ, Herzog CA, Ishani A, Kalra PA. Serum phosphorus levels associate with coronary atherosclerosis in young adults. J Am Soc Nephrol. 2009;20(2):397–404. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 19.Heine GH, Seiler S, Fliser D. FGF-23: the rise of a novel cardiovascular risk marker in CKD. Nephrol Dial Transplant. 2012;27(8):3072–3081. [DOI] [PubMed] [Google Scholar]
- 20.Wolf M. Update on fibroblast growth factor 23 in chronic kidney disease. Kidney Int. 2012;82(7):737–747. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 21.Amann K, Tornig J, Kugel B, et al. Hyperphosphatemia aggravates cardiac fibrosis and microvascular disease in experimental uremia. Kidney Int. 2003;63(4):1296–1301. [DOI] [PubMed] [Google Scholar]
- 22.The Aric I. The Atherosclerosis Risk in Communities (ARIC) Study: Design and Objectives. Am J Epidemiol. 1989;129(4):687–702. [PubMed] [Google Scholar]
- 23.Lutsey PL, Eckfeldt JH, Ogagarue ER, Folsom AR, Michos ED, Gross M. The 25-hydroxyvitamin D3 C-3 epimer: distribution, correlates, and reclassification of 25-hydroxyvitamin D status in the population-based Atherosclerosis Risk in Communities Study (ARIC). Clin Chim Acta. 2015;442(0):75–81. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 24.Tang W, Yao L, Roetker NS, et al. Lifetime Risk and Risk Factors for Abdominal Aortic Aneurysm in a 24-Year Prospective Study: The ARIC Study (Atherosclerosis Risk in Communities). Arterioscler Thromb Vasc Biol. 2016;36(12):2468–2477. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 25.Lutsey PL, Rasmussen-Torvik LJ, Pankow JS, et al. Relation of Lipid Gene Scores to Longitudinal Trends in Lipid Levels and Incidence of Abnormal Lipid Levels Among Individuals of European Ancestry: The Atherosclerosis Risk in Communities (ARIC) Study. Circulation Cardiovascular Genetics. 2012;5(1):73–80. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 26.Inker LA, Schmid CH, Tighiouart H, et al. Estimating Glomerular Filtration Rate from Serum Creatinine and Cystatin C. New England Journal of Medicine. 2012;367(1):20–29. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 27.Lutsey PL, Michos ED, Misialek JR, et al. Race and Vitamin D Binding Protein Gene Polymorphisms Modify the Association of 25-Hydroxyvitamin D and Incident Heart Failure: The ARIC (Atherosclerosis Risk in Communities) Study. JACC Heart Fail. 2015;3(5):347–356. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 28.Peacock M. Calcium metabolism in health and disease. Clin J Am Soc Nephrol. 2010;5 Suppl 1(Supplement 1):S23–30. [DOI] [PubMed] [Google Scholar]
- 29.Calvi LM, Bushinsky DA. When is it appropriate to order an ionized calcium? J Am Soc Nephrol. 2008;19(7):1257–1260. [DOI] [PubMed] [Google Scholar]
- 30.Ross AC, Taylor CL, Yaktine AL, Del Valle HB, Committee to Review Dietary Reference Intakes for Vitamin D and Calcium Dietary reference intakes for calcium and vitamin D: Institute of Medicine. National Academies Press; (Washington DC: );2011. [PubMed] [Google Scholar]
- 31.Holick MF, Binkley NC, Bischoff-Ferrari HA, et al. Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2011;96(7):1911–1930. [DOI] [PubMed] [Google Scholar]
- 32.Martorell S, Hueso L, Gonzalez-Navarro H, Collado A, Sanz MJ, Piqueras L. Vitamin D Receptor Activation Reduces Angiotensin-II-Induced Dissecting Abdominal Aortic Aneurysm in Apolipoprotein E-Knockout Mice. Arterioscler Thromb Vasc Biol. 2016;36(8):1587–1597. [DOI] [PubMed] [Google Scholar]
- 33.Wong YYE, Flicker L, Yeap BB, McCaul KA, Hankey GJ, Norman PE. Is Hypovitaminosis D Associated with Abdominal Aortic Aneurysm, and is There a Dose–response Relationship? European journal of vascular and endovascular surgery : the official journal of the European Society for Vascular Surgery. 2013;45(6):657–664. [DOI] [PubMed] [Google Scholar]
- 34.Bosworth C, Sachs MC, Duprez D, et al. Parathyroid hormone and arterial dysfunction in the multi-ethnic study of atherosclerosis. Clin Endocrinol (Oxf). 2013;79(3):429–436. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 35.Reid IR, Bolland MJ. Calcium supplements: bad for the heart? Heart. 2012;98(12):895–896. [DOI] [PubMed] [Google Scholar]
- 36.Yamanouchi D, Takei Y, Komori K. Balanced mineralization in the arterial system: possible role of osteoclastogenesis/osteoblastogenesis in abdominal aortic aneurysm and stenotic disease. Circ J. 2012;76(12):2732–2737. [DOI] [PubMed] [Google Scholar]
- 37.Anderson JJB, Kruszka B, Delaney JAC, et al. Calcium Intake From Diet and Supplements and the Risk of Coronary Artery Calcification and its Progression Among Older Adults: 10‐Year Follow‐up of the Multi‐Ethnic Study of Atherosclerosis (MESA). Journal of the American Heart Association. 2016;5(10). [DOI] [PMC free article] [PubMed] [Google Scholar]
- 38.Kantor ED, Rehm CD, Du M, White E, Giovannucci EL. Trends in Dietary Supplement Use Among US Adults From 1999–2012. JAMA. 2016;316(14):1464–1474. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 39.Gallagher JC, Smith LM, Yalamanchili V. Incidence of hypercalciuria and hypercalcemia during vitamin D and calcium supplementation in older women. Menopause. 2014;21(11):1173–1180. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 40.Faul C, Amaral AP, Oskouei B, et al. FGF23 induces left ventricular hypertrophy. J Clin Invest. 2011;121(11):4393–4408. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 41.Fyfe-Johnson AL, Alonso A, Selvin E, et al. Serum fibroblast growth factor-23 and incident hypertension: the Atherosclerosis Risk in Communities (ARIC) Study. Journal of hypertension. 2016;34(7):1266–1272. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 42.Stevens KK, McQuarrie EP, Sands W, et al. Fibroblast growth factor 23 predicts left ventricular mass and induces cell adhesion molecule formation. Int J Nephrol. 2011;2011:297070. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 43.Mirza MA, Larsson A, Lind L, Larsson TE. Circulating fibroblast growth factor-23 is associated with vascular dysfunction in the community. Atherosclerosis. 2009;205(2):385–390. [DOI] [PubMed] [Google Scholar]
- 44.Yilmaz MI, Sonmez A, Saglam M, et al. FGF-23 and vascular dysfunction in patients with stage 3 and 4 chronic kidney disease. Kidney Int. 2010;78(7):679–685. [DOI] [PubMed] [Google Scholar]
- 45.Manghat P, Fraser WD, Wierzbicki AS, Fogelman I, Goldsmith DJ, Hampson G. Fibroblast growth factor-23 is associated with C-reactive protein, serum phosphate and bone mineral density in chronic kidney disease. Osteoporos Int. 2010;21(11):1853–1861. [DOI] [PubMed] [Google Scholar]
- 46.Munoz Mendoza J, Isakova T, Ricardo AC, et al. Fibroblast growth factor 23 and Inflammation in CKD. Clin J Am Soc Nephrol. 2012;7(7):1155–1162. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 47.Chun RF, Peercy BE, Orwoll ES, Nielson CM, Adams JS, Hewison M. Vitamin D and DBP: the free hormone hypothesis revisited. J Steroid Biochem Mol Biol. 2014;144 Pt A(0):132–137. [DOI] [PMC free article] [PubMed] [Google Scholar]