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ORIGINAL ARTICLE
The Effects of 3 Years of Calcium Supplementation on Common Carotid Artery Intimal Medial Thickness and Carotid Atherosclerosis in Older Women: An Ancillary Study of the CAIFOS Randomized Controlled Trial Joshua R Lewis,1,2 Kun Zhu,1,2 Peter L Thompson,3 and Richard L Prince1,2 1
School of Medicine and Pharmacology, Sir Charles Gairdner Hospital Unit, University of Western Australia, Nedlands, Australia Department of Endocrinology and Diabetes, Sir Charles Gairdner Hospital, Nedlands, Australia 3 Department of Cardiology, Sir Charles Gairdner Hospital, Nedlands, Australia 2
ABSTRACT Calcium is an essential nutrient for skeletal health; however, it has been suggested that supplemental calcium may be associated with adverse cardiovascular effects, raising widespread concern about their use. One suggested mechanism is via increasing carotid atherosclerosis, however few randomized controlled trials (RCT) of calcium supplements have assessed these mechanisms. The calcium intake fracture outcome study (CAIFOS) was a 5‐year RCT (1998 to 2003) of 1.2 g of elemental calcium in the form of calcium carbonate in 1460 elderly women. An ancillary study of 1103 women assessed common carotid artery intimal medial thickness (CCA‐ IMT) and carotid atherosclerosis at year 3 (2001). The effects of supplementation were studied in intention‐to‐treat (ITT) and per‐ protocol (PP) analyses before and after adjustment for baseline cardiovascular risk factors. The mean age of participants at baseline was 75.2 2.7 years. In ITT analyses, women randomized to calcium supplementation had no difference in multivariable‐adjusted mean CCA‐IMT (calcium 0.778 0.006 mm, placebo 0.783 0.006 mm, p ¼ 0.491) and maximum CCA‐IMT (calcium 0.921 0.007 mm, placebo 0.929 0.006 mm, p ¼ 0.404). Women randomized to calcium did not have increased carotid atherosclerosis (calcium 47.2%, placebo 52.7%, p ¼ 0.066). However, in women taking at least 80% of the supplements, a significant reduction in carotid atherosclerosis was observed in unadjusted but not in multivariate‐adjusted models (p ¼ 0.033 and p ¼ 0.064, respectively). Participants in the highest tertile of total calcium (diet and supplements) had reduced carotid atherosclerosis in unadjusted and multivariable‐adjusted analyses compared with participants in the lowest tertile (odds ratio [OR] ¼ 0.67 [95% confidence interval (CI) 0.50–0.90], p ¼ 0.008, and OR ¼ 0.70 [95% CI 0.51–0.96], p ¼ 0.028, respectively). In conclusion, these findings do not support the hypothesis that calcium supplementation increases carotid artery intimal medial thickness or carotid atherosclerosis, and high calcium intake may reduce this surrogate cardiovascular risk factor. © 2014 American Society for Bone and Mineral Research. KEY WORDS: CALCIUM SUPPLEMENTATION; COMMON CAROTID ARTERY INTIMAL MEDIAL THICKNESS; CAROTID ATHEROSCLEROSIS; HEART DISEASE RISK
Introduction
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alcium is a widely used dietary supplement for the prevention of age‐related bone loss in the elderly.(1,2) The recent Institute of Medicine review of the scientific literature concluded that the available scientific evidence supports a key role of calcium and vitamin D in the maintenance of skeletal health and recommends a daily intake of 1200 mg calcium with 800 IU of vitamin D in the elderly.(3) Calcium supplementation has been shown to reduce blood pressure(4) and may improve energy balance and body composition;(5) however, recently the safety of calcium for extraskeletal outcomes, in particular cardiovascular disease outcomes in the elderly, has been questioned. Given the widespread use of calcium supplementa-
tion, even small increases in cardiovascular risk factors could have major public health implications. Human arteries are comprised of three layers: the intima, the media, and the adventitia. The intima is the innermost layer of the artery and is composed of connective tissue, whereas the media is the wall of the artery and consists of layers of smooth muscle cells. The outermost layer, the adventitia, is highly vascular and comprised of a dense collagenous structure and thus provides much of the nutrition needed for the vessel wall. Atherosclerosis occurs principally in the intima of medium‐sized and large arteries such as the coronary, carotid, vertebral, aortic, and iliac arteries. Early lesions typically begin in childhood and early adulthood and primarily consist of lipid‐laden macrophages and smooth muscle cells that can be distinguished from
Received in original form August 30, 2013; revised form October 7, 2013; accepted October 14, 2013. Accepted manuscript online October 23, 2013. Address correspondence to: Joshua Lewis, PhD, School of Medicine and Pharmacology, University of Western Australia, Sir Charles Gairdner Hospital, Hospital Avenue, Nedlands, Perth, WA 6009, Australia. E‐mail:
[email protected] For a Commentary on this article, please see Bauer (J Bone Miner Res. 2014;29:531–533. DOI: 10.1002/jbmr.2184). Journal of Bone and Mineral Research, Vol. 29, No. 3, March 2014, pp 534–541 DOI: 10.1002/jbmr.2117 © 2014 American Society for Bone and Mineral Research
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normal artery as areas of discoloration on the vessel wall and will either disappear or progress further to become atherosclerotic lesions that worsen with age.(6) Advanced atherosclerotic lesions form fibrous plaques composed of smooth muscle cells, lipid‐ laden macrophages, and T lymphocytes and appear as raised white areas in the vessel wall that are easily visualized using either invasive or noninvasive imaging modalities.(7) B‐mode carotid ultrasound is a noninvasive, sensitive, and highly reproducible modality that measures the distance from the lumen‐intima interface to the media‐adventitia interface of the carotid wall, giving a measure of the carotid intimal medial thickness and presence of focal plaques. It is considered a surrogate measure to quantify subclinical carotid calcification and atherosclerosis, and it is considered a cardiovascular disease risk factor.(8–11) The objective of this study was to use B‐mode carotid ultrasound data from an ancillary study of 1103 elderly women enrolled in the CAIFOS randomized controlled trial to investigate whether 3 years of calcium supplementation increased carotid artery intimal medial thickness (CCA‐IMT) and carotid atherosclerosis.
Materials and Methods Participants The participants involved in this study were recruited in 1998 to a 5‐year, randomized, controlled trial of oral calcium supplements to prevent osteoporotic fractures as described previously.(12) Briefly, women were recruited from the Western Australian general population of women older than 70 years by mail using the electoral roll, a requirement of citizenship. More than 99% of Australians of this age are registered on the roll. Of the 5586 women who responded to a letter inviting participation, 1510 women were willing and eligible, and, of these, 1460 women were recruited for the study. Participants were ambulant and did not have any medical conditions likely to influence 5‐year survival. They were excluded if they were receiving bone‐active agent, including hormone replacement therapy. Participants were similar in terms of disease burden and pharmaceutical consumption to whole populations of this age, but they were more likely to be from higher socioeconomic groups.(13) In the 5 years of the trial, participants received 1.2 g of elemental calcium as calcium carbonate daily or a matched placebo. A preplanned ancillary study at year 3 to investigate epidemiological determinants of CCA‐IMT and carotid atherosclerosis by B‐ mode carotid ultrasound examination was undertaken in 1103 participants of the original cohort. Informed consent was obtained, and the Human Ethics Committee of the University of Western Australia approved the study.
Overview of Calcium Intake Fracture Outcome Study (CAIFOS) randomized controlled trial Patients received calcium carbonate tablets, 0.6 g twice per day (with morning and evening meals), or identical placebo tablets (Wyeth Consumer Healthcare, Baulkham Hills, Australia). The randomization list was produced by generating 146 blocks of 10 numbers. In each block, 5 positions representing placebo and 5 positions representing calcium treatment were ordered using a letter code according to a random number generator. The numbered blocks were ordered according to randomly generated numbers, and an identification number was assigned to each letter code in the randomized list. The Pharmacy Department of
Journal of Bone and Mineral Research
the Sir Charles Gairdner Hospital (Nedlands, Australia) assigned a treatment to the letter code and assigned the appropriate medications to the patient according to this list. The randomization was stratified by allocating patients to blocks according to whether a prevalent nontraumatic fracture had occurred after age 50 years, ensuring that an equal number of patients with and without a prevalent fracture received placebo or calcium. Medication compliance was checked at the completion of the study by counting returned tablets at each 12‐month review and was calculated as a percentage of the optimum. Average yearly compliance of less than 80% was classified as noncompliant.
Baseline atherosclerotic vascular disease (ASVD) risk assessment The participants provided their previous medical history and current medications verified by their general practitioner. These data were coded using the International Classification of Primary Care‐Plus (ICPC‐Plus) method.(14) The coding methodology allows aggregation of different terms for similar pathologic entities as defined by the International Classification of Disease (ICD)‐10 coding system. These data were then used to determine the presence of preexisting diabetes (T89001‐90009). Cardiovascular medications included beta‐blockers, angiotensin‐converting enzyme inhibitors, angiotensin II receptor blockers, HMG‐Co A reductase inhibitors, and antiplatelet agents. Smoking status was coded as nonsmoker or ex‐smoker/current smoker if they had consumed more than one cigarette per day for more than 3 months at any time in their life. Weight was assessed using digital scales with participants wearing light clothes and no shoes. Height was assessed using a stadiometer, and the body mass index (BMI) was calculated in kg/m2 at baseline. Blood pressure was measured on the right arm with a mercury column manometer using an adult cuff after the participants have been seated in an upright position and had rested for 5 minutes. An average of three blood pressure readings was recorded. Mean arterial pressure (MAP) was calculated using the following equation: [(2 diastolic blood pressure) þ systolic blood pressure]/3.
Dietary calcium intake A validated semiquantitative food‐frequency questionnaire developed by the Cancer Council of Victoria was used to assess baseline dietary intake, including calcium(15) in 1050 of 1103 (95.2%) of participants. The process of collection was identical, whereby a research assistant supervised the completion of the questionnaire in small groups. Food models, cups, spoons, and charts for frequency were provided. Energy and nutrient intakes were estimated based on frequency of consumption and an overall estimate of usual portion size.(16) Total supplemental calcium intake was calculated by multiplying the overall study percentage tablet compliance by 12 to convert to mg/d and adding dietary calcium intake in mg/d to provide a total calcium intake (mg/d).
Biochemical assessment Blood samples were collected at baseline for assessment. Plasma 25‐hydroxy vitamin D3 (25OH‐D3) concentrations were determined using liquid chromatography tandem mass spectrometry method (RDDT Laboratories, Melbourne, Australia) using the Agilent 6410 Triple Quadrupole LC‐MS/MS. Total cholesterol, high‐density lipoprotein cholesterol (HDLC), and triglyceride concentrations were determined using a Hitachi 917 auto analyzer (Roche Diagnostics, Mannheim, Germany). Low‐density
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lipoprotein cholesterol (LDLC) was calculated using Friedewald’s method.(17) Baseline creatinine was measured using an isotope dilution mass spectrometry (IDMS) traceable Jaffe kinetic assay on a Hitachi 917 analyzer (Roche Diagnostics). Estimated glomerular filtration rate (eGFR) using creatinine was calculated using the Chronic Kidney Disease Epidemiology Collaboration (CKD‐EPI) equation(18) and was added to the multivariable‐ adjusted model as this has been shown to predict ASVD in this cohort.(19)
Prevalent atherosclerotic vascular disease Atherosclerotic hospitalizations were retrieved from the Western Australian Data Linkage System (WADLS) for each of the study participants from 1980 to 1998. WADLS provides a complete validated record of every participant’s hospitalizations from the coded records of each participant’s hospital admissions. Atherosclerotic events were defined using the principal discharge diagnosis codes from the International Classification of Diseases, Injuries and Causes of Death Clinical Modification (ICD‐9‐CM).(20) These codes included: ischemic heart disease (ICD‐9‐CM codes 410–414); heart failure (ICD‐9‐CM code 428); cerebrovascular disease excluding hemorrhage (ICD‐9‐CM codes 433–438); and peripheral arterial disease (ICD‐9‐CM codes 440–444).
B‐mode carotid ultrasound The presence of carotid focal plaques and common carotid artery intimal medial thickness (CCA‐IMT) were determined at year 3. Assessments were performed using B‐mode carotid ultrasound examination by the same sonographer with an 8.0‐mHz linear array transducer fitted to an Acuson Sequoia 512 (Mountain View, CA, USA) ultrasound machine using a standard image acquisition protocol in 2001.(21) The far walls of the distal 2 cm of the left and right common carotid arteries were examined, and images were taken from three different angles (anterolateral, lateral, and posterolateral) to account for the possibility of asymmetrical wall thickening. End‐diastolic images were recorded and a semi‐automated edge‐detection software program was used for image analysis. The same technician performed offline analysis of all of the images. After assessment of CCA‐IMT and focal plaque on the right side, the process was repeated on the left side. The CCA‐IMT from each of the six images (three on either side) was averaged to give an overall mean CCA‐IMT. Once IMT images were recorded, the entire carotid tree (CCA, carotid bulb, internal and external carotid) was examined for the presence of focal plaque, defined as a clearly identified area of focal increased thickness (1 mm) of the intima‐media layer. A short‐term precision study of 20 nontrial subjects with repeat IMT measurements between 0 and 31 days apart (mean 10.3 days) was performed, which yielded a coefficient of variation of 5.98% as described previously.(22)
Statistics Mean or maximum CCA‐IMT was a continuous variable (mm), whereas the presence of a carotid atherosclerotic plaque was used as a dichotomous (yes/no) variable. Baseline characteristics were stratified by treatment groups (calcium and placebo), and were expressed as mean and standard deviation (SD) for continuous variables or as number and percentage for categorical variables. For presence of an atherosclerotic plaque, unadjusted and multivariable‐adjusted logistic regression models were used to examine the effects of calcium supplementation
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(yes/no) on atherosclerotic plaque (yes/no) with results expressed as odds ratios (OR) and 95% confidence intervals (CI). To investigate a “dose” relationship between dietary calcium and calcium supplements, tertiles of total calcium intake were calculated and tested in unadjusted and multivariable‐adjusted analyses. The covariates in the multivariable‐adjusted models included age, BMI, smoking history, cardiovascular disease medications, diabetes, history of clinical ASVD, and estimated glomerular filtration rate by the CKD‐EPI equation. Analyses were undertaken using SPSS (version 18; SPSS Inc., Chicago, IL, USA) and SAS (version 9, SAS Institute Inc., Cary, NC, USA) programs. Any p values
