**2. Patients and methods**

**1. Introduction**

74 A Critical Evaluation of Vitamin D - Clinical Overview

of vitamin D.

ceptible [9, 10].

dently associated with lower Vit D levels [17].

and potential synergistic action with statins has been reported [18].

Vitamin D (Vit D) plays an important role in normal physiological function and is essential for bone mineralization [1]. Recently, Vit D deficiency is under consideration due to the fact that it has been associated with cardiovascular disorders, malignancy, fractures and deaths [2–4]. Vit D deficiency represents an important public health concern which is commonly observed worldwide [5–7]. Vit D deficiency remains an underrecognized problem in the general populace and is poorly defined in elderly patients. This phenomenon results from reduced capacity of the skin to produce vitamin D, low skin exposure, skin pigmentation, sunscreen use, skin covering clothes and a diet low in fish and dairy products. In the elderly the reduced dermal synthesis of vitamin D is unlikely to be compensated by dietary intake

In a geriatric population, Vit D deficiency has been associated with poor muscular, physical and cognitive physical performance as well as falls and fractures [8]. In a study of community dwelling persons, performed in the Chianti area in the centre of Italy which has a mild pleasant climate and sunlit rural areas, Vit D deficiency was found to be significantly high. Vitamin D levels (VDL) noticeably lessens with age in both males and females alike, but then the decline starts substantiality earlier and is sharper in females starting from the perimenopausal age. In males the decline in vitamin D levels becomes apparent 20 years later starting from their 70s, Vit D deficiency is significantly associated with aging and elderly patients who need hospitalization for longer periods and as a result more sus-

Advanced age and low exposure to sunlight are the major factors associated with Vit D deficiency. Van der Wielen et al. [11] found that regardless of geographical location, free-living elderly (>70 years) living in 11 European countries are at substantial risk of inadequate Vit D status during winter and spring time and in the oldest and more obese subjects. In fact, 86% of these subjects with multiple risk factors were vitamin D deficient. Several studies have

A report from Kuwait showed subclinical Vit D deficiency among veiled women [16]. Also, reports from Saudi Arabia demonstrated higher Vit D deficiency in Saudi women. The authors found female gender, sedentary lifestyle and low milk consumption to be indepen-

In a previous study from Qatar, El-Menyar et al. reported a high percentage (91%) of low Vit D level (<30 ng/ml) in adults (mean age: 49 ±12 years); they also found a strong association between low Vit D and hypertension [14]. Several studies addressed the association between low Vit D and high triglyceride (TG) levels, low levels of high density lipoprotein (HDL-C) and the quality of HDL [18]. Furthermore, the interference of 'Vit D' in cholesterol synthesis

Vit D also plays a role in insulin secretion and therefore is associated with type 2 diabetes mellitus (T2DM). Earlier studies suggested a significantly higher risk of T2DM in Vit D–deficient patients [19, 20]. In contrast, Hidayat et al. [21] observed no significant association between

reported Vit D deficiency among different populations from the Middle East [12–15].

#### **2.1. Significance for public health**

Low vitamin D levels have been associated with causing a range of chronic conditions. A few studies have evaluated the prevalence of low vitamin D prominence in Middle Eastern countries like Qatar and its possible correlation with other causes of chronic disease.

Information available recognizes the high prevalence of vitamin D deficiency in Qatar and highlights the need to develop a nationwide illustrative study to evaluate further. Subsequently, the study may assist in the development of public health strategies for the prevention of diseases in Qatar.

#### **2.2. Study setting**

This study was conducted between April 2010 and April 2012 and involved data collected from elderly patients (65 years). Geriatric patients 65 years and above in healthcare facilities in Qatar were considered as the sample group; serum total 25-hydroxyvitamin D (25(OH) D) levels were measured, individual patient characteristics, treatment plans, treatment and results were analysed and compared in order of diagnosed Vit D deficiency severity. Patients who had not been screened for Vit D levels or who had incomplete data were excluded.

#### **2.3. Measures**

A data-extraction tool was developed that built in information relating to demographics, body mass index (BMI, calculated based on height and weight; kg/m2 ) and blood examinations (full blood count, serum albumin, calcium, phosphorus, comorbidities, medications, and outcome).

An immunoanalyser (Liaison, Diasorin Inc.) was used for the measurement of Vit D. 'It is an automated direct competitive chemiluminescence immunoassay (CLIA) for quantitative determination of total 25-OH Vit D in serum or plasma. The imprecision at 56 and 19 ng/ml as measured by coefficient of variation was 8.7 and 13.2%, respectively [14]'.

The Diazyme's 25(OH) D assay is one of the fast track diagnostic methods with complete testing results in less than 2 hours. 'The test is user-friendly, and can be performed manually or easily adapted for use on a wide range of fully automated microtiter plate readers, making it suitable for use in laboratories of all sizes and with all manner of testing needs'.

Vit D deficiency was defined as level less than 30 ng/ml which was further subdivided into mild (20–29 ng/ml), moderate (10–19 ng/ml) and severe insufficiency (less than 10 ng/ml) [14, 21]. Patient characteristics and outcomes were analysed and compared according to the severity of Vit D deficiency. Patients after 6 months were re-evaluated for Vit D levels and all-cause mortality.

#### **2.4. Statistical analysis**

Where appropriate, data is presented as proportions, medians or mean ±SD. Wherever applicable the continuous variables were analysed using Student's tests or one-way ANOVA. Also a non-parametric Mann–Whitney test was used for skewed continuous data. Definite variables among groups were compared using the chi-square test; estimating the associations between Vit D deficiency and demographic and clinical index. Age and its correlation with HDL-C, HbA1c and Vitamin D levels was also studied using Pearson's correlation method.

A two adjusted *P* < 0.05 was considered significant. All data investigation was carried out using the Statistical Package for Social Sciences version 18 (SPSS Inc., USA).
