Study of bone mineral density and their determinants among Medical practitioners of a Tertiary care Government hospital

Introduction

Medical practitioners are a set of people having erratic lifestyles, irregular dietary patterns, poor physical activity and poor exposure to sunlight¹. Hence, they form a vulnerable population for reduced Bone Mineral Density (BMD). Peak bone mass, a major determinant of osteoporosis is influenced by genetic, nutritional, lifestyle and hormonal factors² . Vitamin D deficiency prevails in epidemic proportions all over the Indian subcontinent, with a prevalence of 70%–100% in the general population³ . The Indian population appears particularly vulnerable to the problem of osteoporosis and hip fractures and develop these conditions almost a decade earlier than their Caucasian counterparts⁴ . Bone Mineral Density is further compromised by conditions like Type 2 Diabtes Mellitus whose incidence is on the rise⁵ . Pure vegetarian diet and higher melanin content among the study population may also contribute to decreased serum Calcium and Vitamin D levels respectively⁶ . The best way to prevent deterioration of Bone Mineral Density and its possible complications like osteoporosis is to screen the population for BMD values at regular intervals. Hence we carried out this study in our hospital set up by which we have obtained a picture of the prevailing bone health and its determinants among medical practitioners in the study setting. Estimation of BMD values and their correlation with serum levels of Calcium, vitamin D and other factors like physical activity, diet and sun exposure can go a long way in documenting and treating subjects at risk for complications and morbidity. It can play a significant role in keeping the healthcare system healthy. Hence the present study was aim to test Bone Mineral Density (BMD) values using Dual Energy X-Ray Absorptimetry (DEXA) scan among the study population and to correlate values of Bone Mineral Density with serum 25-(OH) cholecalciferol, serum calcium, weight, height, body mass index (BMI), sun exposure, physical activity and diet and also to document known co-morbidities among study population.

Materials and methods

The study is a prospective cross sectional study. It was conducted between July 1st to August 31st,2017. 50 medical practitioners adhering to the inclusion and exclusion criteria of the study were invited for participation with voluntary consent. Their Bone Mineral Density values were calibrated by using an Ultrasound based Bone mineral densitometer having a 1 MHz transducer probe. The values were calibrated by probing ‘tibia’ bone and have been expressed in terms of T scores (corresponds to standard deviation). The values were also graded into 3 categories – normal (0 to -1.0), osteopenic (-1.1 to -2.5) and osteoporotic (-2.6 to -4.0) according to WHO guidelines. DEXA scan could not be used for the study due to constraints in availability and funding of the process. Ultrasound based values are closely comparable to values obtained by DEXA scan and hence the study objective has been adhered to in the best possible manner.

Subsequently the blood samples of the participants were collected at the same venue. 3 ml syringes were used with all necessary aseptic precautions. Tributaries of the cephalic vein were selected for withdrawal of blood. The samples were transferred immediately into sterile vacutainer tubes and were labeled. No anticoagulant was used. They were transported to the biochemical laboratory within a time of 2 hours of collection. Serum Vitamin D (25-OH Cholecalciferol) values were estimated by radioimmunoassay method and were expressed in nmol/L. The values were graded as normal (>50), normal/high bone turnover (25-50), high bone turnover (12.5-25) and incipient osteomalacia (<12.5).

Serum Calcium values were estimated by semiautoanalyser and were expressed in mg/ dl. The values were graded as normal (>8.9) and hypocalcemic (<8.9).

Body Mass Index values of all the study subjects were compiled after measuring their heights and weights at the venue using the formula

BMI= weight (kg) / (Height (m) 2 . The values were graded as normal (18.5-23.9), underweight (<18.5), overweight (24-29.99) and obese (>30).

Sun exposure was calculated by calculating ‘Sun Index’ which is expressed as the product of hours of sun exposure per day and the percentage of body surface area exposed per day.

Physical activity was expressed as moderate (3-6 MET) or severe (>6 MET) physical activity based on responses to a questionnaire on the same.

Results

50 study subjects (25 males and 25 females) were invited to participate in the study. Average age of the study population was 40.2. The age distribution is illustrated below-

Bone Mineral Density (BMD) values computed using bone densitometer showed an average BMD value of -1.156 (T score) which falls in ‘osteopenic’ range. The distribution of BMD values in the study population is illustrated below-

Serum Vitamin D (25-OH cholecalciferol) values estimated by semiautoanalyser were computed and 88% of the study population was found to be vitamin D deficient (<50 nmol/L). 58% of subjects had values between 25-50 nmol/L and 30% had values between 12.5-25 nmol/L. The distribution of vitamin D values in the study population is illustrated below-

Serum Calcium values estimated by radioimmunoassay method were compiled and they showed an average value of 9.35 mg/dl which falls within the normal range. The distribution of serum calcium values in the study population is illustrated below

Comparison of serum Vitamin D and BMD values was made. We found that there was no significant association between the two parameters. In other words, low values of serum Vitamin D do not directly correlate with low BMD values in the study population.

Comparison of serum calcium values and BMD was made. There was no significant association between the two parameters. Low serum Calcium values did not directly correlate with low BMD values.

A comparison between serum calcium and serum vitamin D levels was made. There was no significant association between the two parameters and hence serum vitamin D and calcium values do not seem to influence each other.

Gender predisposition of low Vitamin D and low BMD values was examined. Slight female preponderance was found among the subjects having low values of serum Vitamin D and BMD. The results are illustrated below

A comparison was made between Body Mass Index (BMI) and BMD values. It was found that 62.5 % of subjects above the normal upper limit BMI of 24 had low Bone Mineral Density values. Hence it is clear that low BMI values are more likely to be associated with healthier BMD values.

A comparison was made between Sun Exposure and BMD values. In both the groups with sun index greater than and lesser than 20, the proportion of people with normal BMD was greater- 60% of subjects with sun index > 20 and 53.3% of subjects with sun index < 20 had normal BMD. The results are illustrated below-

A comparison was made between skin type and Bone Mineral Density. 40 out of the 50 participants (80%) had skin type 3-6. 57.5% of people with skin type 3-6 had normal BMD and 42.5% had low BMD. 60% of subjects having skin types 1 and 2 had normal BMD and 40% had low BMD. The results are illustrated below-

Discussion

Our study was started with the aim of estimating Bone Mineral Density (BMD) values among medical practitioners of a tertiary care government hospital and correlating it with serum parameters like vitamin D, calcium and other parameters like Body Mass Index, Sun exposure and Physical activity. We chose an equal number of male and female participants for the study (25 participants each). Mean age of the participants of the study was 40.2 years.

Bone Mineral Density (BMD) estimation showed an average T score of -1.156 which falls in the osteopenic range. 42% of study subjects were found to be osteopenic. In the study by Multani S K et al 1131 out of 214 study subjects (61.2%) who were also medical practitioners were osteopenic. In the study conducted by Sunil Kota et al⁸ around 43.1% of participants were osteopenic. None of the subjects in our study was found to be osteoporotic which may have to do with the lower mean age of participants. BMD values are expected to decrease in the mid thirties and the decrease is expected to accelerate around menopause in women 4 .

Serum vitamin D estimation among the study population showed the following – 88% of our study population had low values of vitamin D (< 50 nmol/L) and 12% had values in the normal range. Vitamin D deficiency is believed to be prevalent to the extent of 70-100% among Indian population³ . In the study conducted by Sunil kota et al⁸ . 84.3% of subjects had vitamin D deficiency. When we correlated Vitamin D and BMD values, we found that there was no significant association between the two – P(0.05) was 1.703 which is insignificant. The above mentioned study by Sunil Kota et al. also came to the conclusion that there was no significant association between vitamin D and BMD values. The study by VasundharaKamineni et al9 also concluded that there was no correlation between Vitamin D and BMD values.

Serum Calcium estimation showed that 90% of study subjects had values in the normal range (8.9- 10.3 mg/dl). 6% of the population had low serum calcium level. Correlation between serum calcium and BMD values was made. We found that the association between the two was insignificant – P(0.05) was 0.797 which was insignificant. The studies mentioned in the ‘references’ section also broadly coincide with the conclusion that there is no correlation between serum calcium and BMD.

Body Mass Index (BMI) values were computed among the study population and it showed that 48% of the study population had BMI in excess of 24. Among this group 62.5 % of people had low BMD and 37.5% had normal BMD values. Among the population with BMD < 24, 70% had normal BMD and 30% had low BMD values. Hence lower values of BMI were found to be associated with healthier values of BMD. This conclusion was also made by a study conducted by Mohammad Reza Salamat et al¹²and in another one conducted by RexhepHoxha et al.¹³

Sun exposure among the study population was computed using the Sun Index. The population was divided into 2 groups based on an arbitrary cut off value of 20 and it was found that in people with sun index < 20, 53.3% of people had normal BMD values and 46.7% of people had low BMD values. Among the subjects with sun index > 20, 60% had normal BMD and 40% had low BMD. Though the BMD values in subjects with higher sun exposure are slightly better than the ones with lesser exposures, data does not suggest significantly better BMD values in subjects with higher exposure to sunlight. A study conducted by Weaver S P et.al also concluded that there was no significant improvement in vitamin D levels in their study subjects even after 6-8 weeks of sun exposure¹⁴.

Conclusion

The Bone Mineral Density (BMD) values in the study population are on an average in the osteopenic range. Low serum vitamin D levels (in 88% of the subjects), higher values of Body Mass Index (in 48% of subjects), lesser exposure to sunlight and darker skin types seem to be determining factors for BMD as suggested in some of the references, but in our study we did not find significant association between BMD values and serum parameters such as Vitamin D and Calcium. Although low BMI and higher exposure to sunlight correlate with higher BMD values, the association is again not significant. The cause for lower values of BMD and vitamin D seems to be multifactorial and not strongly associated with any one parameter.