Preoperative Vitamin D Status in Potential Bariatric Surgery Patients

Abstract

Background:

Vitamin D deficiency has been described in a variety of population groups. Specifically, the vitamin D status in pre-operative bariatric patients is a growing concern in the field of weight reduction surgery, where gastric bypass may exacerbate a preexisting deficiency or insufficiency.

Objectives:

The purpose of this study was to determine the vitamin D status in pre-operative bariatric patients and to compare results according to race, gender, Body Mass Index, and age. Setting: Medical University of South Carolina, Charleston, South Carolina. Methods: Our study cohort included 235 morbidly obese adult patients who presented for bariatric surgery. Serum levels of 25-hydroxy vitamin D were tested and categorized as insufficient (20–80 nmol/L or 8–32 ng/mL), deficient (15–20 nmol/L or 6–8 ng/mL), or severely deficient (<15 nmol/L or 6 ng/mL). Results were compared by BMI groups (35–39.9, 40–49.9, 50–59.9, or > 60 in kg/m²), age groups (<35, 36–45, 46–55, 56–65, or >65), race (black or white), and gender.

Results:

Thirty-six percent of our cohort had severe vitamin D deficiency, and the remaining 64% were deficient or insufficient in vitamin D. Results showed a statistical difference among the three vitamin D categories for BMI, race, and gender groups but not between age groups.

Conclusion:

Introduction

According to the National Health and Nutrition Examination Survey (NHANES) of 1999–2002, the prevalence of overweight or obesity among Americans older than 20 years remains high with 65.1% classified as overweight or obese (this includes all subjects with a BMI > 25.0 kg/m²), 30.4% as obese (BMI > 30.0 kg/m²), and 4.9% as extremely obese (BMI > 40.0 kg/m²).¹

With an increase in BMI comes an increase in the burden of diseases, including type 2 diabetes mellitus, gallbladder disease, coronary heart disease, high blood cholesterol levels, high blood pressure, and osteoarthritis. There is an increase in the prevalence of multiple health conditions as weight status increases.² Further, obesity leads to years of life lost, particularly as BMI increases or as the age at which a person becomes obese decreases.³

In response to ballooning obesity rates, a variety of restrictive and malabsorptive bariatric surgery procedures have been developed to restrict the caloric intake of patients seeking large-scale weight reduction. In 1991, the National Institutes of Health issued a consensus statement on gastrointestinal surgery for severe obesity and determined that bariatric surgery is appropriate for the treatment of morbid obesity in persons with a BMI of 35–40 kg/m² and weight-related comorbidities or with a BMI > 40 kg/m² when conventional weight loss attempts have failed.⁴ An estimated 205,000 bariatric surgeries were performed in 2007, a 70% increase from the number of procedures that were performed in 2003.⁵ Of those, 80% of weight loss procedures were the Roux-en-Y gastric bypass. Through the creation of a negative energy balance in obese individuals, bariatric surgery is a proven method for inducing significant weight loss with excellent long-term results.

The Roux-en-Y gastric bypass promotes weight loss via restrictive and malabsorptive mechanisms. The stomach size is reduced to approximately 15–30 mL, which restricts food intake, and the bypassing of the remaining gastric body, duodenum, and proximal jejunum promotes malabsorption of macronutrients.⁷ While the overall goal of weight loss following gastric bypass is improved health and longevity, the mechanisms of action of this procedure also increase the risk for micronutrient deficiencies, particularly of B vitamins, including thiamin, folate, and vitamin B12; minerals such as iron and calcium; and fat-soluble vitamins like vitamin D and vitamin A. Further, many obese subjects present for bariatric surgery with deficient or insufficient levels of these nutrients.⁸

The high rates of vitamin D deficiency and insufficiency in both pre- and post-operative bariatric patients is a growing concern in the field of weight reduction surgery.⁹ The relationship between low serum 25-hydroxy vitamin D (25(OH)D) and the long-term risk of metabolic bone disease is perhaps the most thoroughly researched; however, a growing number of studies have indicated possible links between vitamin D deficiency and hypertension, malignancy risk, diabetes mellitus, and heart disease.^10–14

Several studies have already documented an inverse relationship between serum vitamin 25(OH)D and obesity in the general population.^15,16 Additional studies have confirmed high rates of vitamin D deficiency and insufficiency in pre- and post-operative bariatric patients specifically.^10,11 While the exact etiology for low vitamin D in the morbidly obese remains unclear, contributing factors include inadequate intake from dietary sources or supplements, decreased sun exposure, and possible sequestration of vitamin D in adipose tissue. Nonetheless, repletion after a malabsorptive procedure such as gastric bypass is a challenge.

As a result, adequate vitamin D screening and supplementation are critical to maximize the benefits of bariatric surgery on weight-related comorbidities. The purpose of this study is to examine rates of vitamin D deficiency and insufficiency in a university hospital–based bariatric surgery clinic. Specifically, pre-operative vitamin 25(OH)D levels in patients presenting for bariatric surgery are analyzed in subgroups based on race, gender, age, and presenting BMI. Once the prevalence of vitamin D deficiency is better understood in the general population and subpopulations, appropriate screening and intervention can be developed.

Materials and Methods

This was a retrospective descriptive study based on patient data available through the bariatric surgery patient database. Subjects included men and women presenting for preoperative evaluation for bariatric surgery at the Medical University of South Carolina (MUSC) between July 1, 2007, and July 1, 2008, who were older than 18 years at the time of the preoperative evaluation. Data collected from this visit included serum levels of 25-hydroxy vitamin D, presenting BMI, age, self-reported race, and gender. Serum levels of 25-hydroxy vitamin D were tested and categorized as insufficient (20–80 nmol/L or 8–32 ng/mL), deficient (15–20 nmol/L or 6–8 ng/mL), or severely deficient (<15 nmol/L or 6 ng/mL). These categories were based on our treatment protocol. Patients who present with a vitamin D level <15 nmol/L are treated with 50,000 IU of vitamin D once per week for 8 weeks, then once per month for 4 more months and then rechecked. Patients who present with a vitamin D level of 15–20 nmol/L are treated with 50,000 IU of vitamin D once per month for 6 months, then rechecked. While repletion with cholecalciferol (vitamin D3) is preferred, ergocalciferol (vitamin D2) is currently the more available form of prescription-strength (50,000 IU) vitamin D available.

And while patients with a vitamin D level in the range of 20–80 nmol/L are not treated with high-dose vitamin D, the literature supports that levels in this range are not adequate to promote optimum health.^7,8,13 All procedures were approved by the Institutional Review Board at MUSC. Statistical analyses were conducted using SAS Statistical Software (SAS, Cary, North Carolina). Analysis of variance was used for continuous outcomes, and chi-square analysis for categorical outcomes.

Results

Our study cohort included 235 morbidly obese adult patients who presented for bariatric surgery, of which 80% were women, with a mean BMI of 51 kg/m2 (range 37–79 kg/m2). Refer to Table 1 for the population's demographics. Thirty-six percent had severe vitamin D deficiency, and the remaining 64% were deficient or insufficient in vitamin D. The racial-ethnic breakdown of the population was 70% white and 28% African American. Mean vitamin D levels for whites and African Americans were 23 nmol/L (9.2 ng/mL) (sd:10) and 14 nmol/L (5.6 ng/mL) (sd:7), respectively (p < 0.0001). Mean vitamin D level was 21 nmol/L (8.4 ng/mL) (sd:9) for males and 20 nmol/L (8 ng/mL) (sd:10) for females (p = 0.589).

Table 1.

Population Demographics

Demographics
Total_N	235
Female	80%
Male	20%
Race	N (%)
White	70%
Black	28%
Other	2%
Mean Age (sd)	45 (12)
Mean BMI (sd)	51 (9)
BMI Class	N (%)
BMI 35-39.9 kg/m²	6%
BMI 40-49.9 kg/m²	45%
BMI 50-59.9 kg/m²	31%
BMI > 60 kg/m²	18%
Mean Vit D Level (sd)	20 (10) nmol/mL
Vit D Class	N (%)
Insufficient	44%
Deficient	20%
Severely Def	36%

Mean vitamin D levels by BMI groups are illustrated in Table 2. Differences in mean levels did vary among the four BMI groups (p = 0.0009). The main contribution to this statistically significant difference is the difference between the BMI > 60 in kg/m2 group and the BMI 35–39.9 and 40–49.9 groups.

Table 2.

Comparison of Vitamin D Deficiency Group by BMI Class

			BMI Group
		Total_N	35–39.9 kg/m ²	40–49.9 kg/m ²	50–59.9 kg/m ²	>60 kg/m ²
All^*	N	234	14	106	72	42
	% of Table	100.00	5.98	45.30	30.77	17.95
Deficiency Level
DEF	N	46	2	27	8	9
	% of Column	19.66	14.29	25.47	11.11	21.43
	% of Row	100.00	4.35	58.70	17.39	19.57
INSUF	N	104	10	52	32	10
	% of Column	44.35	71.43	49.04	43.66	24.39
	% of Row	100.00	9.62	50.00	30.77	9.62
SEVDEF	N	84	2	27	32	23
	% of Column	35.90	14.29	25.47	44.44	54.76
	% of Row	100.00	2.38	32.14	38.10	27.38

1 subject missing information.

Vitamin D levels were also categorized by deficiency level (i.e., insufficient, deficient, and severely deficient) and compared in univariate analyses by BMI groups (35–39.9, 40–49.9, 50–59.9, or >60 in kg/m2), age groups (<35, 36–45, 46–55, 56–65, or >65 years), race (black or white), and gender (male or female). Results showed a statistical association between vitamin D deficiency and BMI classifications (p < 0.0011; see Table 2). A statistical association was also detected between vitamin D deficiency level and race (p < 0.0001; Table 3) as well as gender (p = 0.0432; Table 4). The proportion of severely deficient blacks (54%) was higher than the proportion of whites (46%), although not statistically significant (p = 0.59). However, in the deficient group, there was a statistically significant difference between the proportion of blacks with a deficient level (23%) compared to the proportion of whites (76%; p = 0.0004). The proportion of females in each deficiency group was always greater than the proportion of males (p < 0.01). Within gender, the proportion of males across the vitamin D deficiency levels did not vary statistically: 44% insufficient, 33% deficient, and 24% severely deficient (p = 0.27). However, within females, differences between the proportions within each deficiency level were detected: 44% insufficient, 17% deficient, and 39% severely deficient (p < 0.0001). A statistical association was not detected with age groups (p = 0.5581; Table 5).

Table 3.

Comparison of Vitamin D Deficiency Group by Race

			Race
		Total_N	BLACK	WHITE
All^*	N	231	65	166
	% of Table	100.00	28.14	71.86
Deficiency Level
DEF	N	46	11	35
	% of Column	19.91	16.92	21.08
	% of Row	100.00	23.91	76.09
INSUF	N	102	9	93
	% of Column	44.16	13.85	56.02
	% of Row	100.00	8.82	91.18
SEVDEF	N	83	45	38
	% of Column	35.93	69.23	22.89
	% of Row	100.00	54.22	45.78

4 subjects missing race information.

Table 4.

Comparison of Vitamin D Deficiency Group by Gender

			Gender
		Total_N	F	M
All	N	235	187	48
	% of Table	100.00	79.57	20.43
Deficiency Level
DEF	N	46	31	15
	% of Column	19.57	16.58	31.25
	% of Row	100.00	67.39	32.61
INSUF	N	104	83	21
	% of Column	44.26	44.39	43.75
	% of Row	100.00	79.81	20.19
SEVDEF	N	85	73	12
	% of Column	36.17	39.04	25.00
	% of Row	100.00	85.88	14.12

Table 5.

Comparison of Vitamin D Deficiency Group by Age

			Age Group
		Total_N	<35 yrs	36–45 yrs	46–55 yrs	56–65 yrs	>65 yrs
All^*	N	229	51	52	73	48	5
	% of Table	100.00	22.27	22.71	31.88	20.96	2.18
Deficiency Level
DEF	N	45	7	7	18	12	1
	% of Column	19.65	13.73	13.46	24.66	25.00	20.00
	% of Row	100.00	15.56	15.56	40.00	26.67	2.22
INSUF	N	101	21	26	29	23	2
	% of Column	44.10	41.18	50.00	39.73	47.92	40.00
	% of Row	100.00	20.79	25.74	28.71	22.77	1.98
SEVDEF	N	83	23	19	26	13	2
	% of Column	36.24	45.10	36.54	35.62	27.08	40.00
	% of Row	100.00	27.71	22.89	31.33	15.66	2.41

6 subjects missing age information.

Discussion

With the rising obesity epidemic and increase in the number of patients presenting for bariatric surgery, the concern about pre- and post-operative micronutrient deficiency in this population also rises. As we learn more about the role of vitamin D in bone health and other chronic diseases, the prevalence of vitamin D deficiency in the general population has generated a lot of interest.

Using NHANES III (1988–1994) data, Looker et al. evaluated the prevalence of vitamin D deficiency (<17.5 nmol/L or 7 ng/mL) and insufficiency (<25 nmol/L or 10 ng/mL) in over 18,000 non-institutionalized individuals older than 12 years.¹⁴ To account for variability of latitude and season of data collection, the sample was divided into two groups: winter/lower latitude (average latitude 32°N) and summer/higher latitude (average latitude 30°N). This study showed little evidence (<1%) of frank deficiency in the general population. However, non-Hispanic blacks had the highest rates of insufficiency, followed by Mexican Americans, compared to non-Hispanic whites. All groups in the winter/lower subpopulation had some level of insufficiency. Prevalence rates were double in females compared to males of the same age. Other age patterns were inconsistent, although “insufficiency occurred fairly frequently in younger individuals, especially in the winter/lower group.”¹⁴

Additional studies have confirmed high rates of vitamin D deficiency and insufficiency in the obese population in general and specifically pre- and post-operative bariatric patients. Arunabh et al. studied 25(OH)D as it related to adiposity in 410 women with BMI 17–30 kg/m² and found that percentage of body fat content is modestly but inversely related to serum vitamin D levels, with mean vitamin D levels of 44.2 nmol/L (17.7 ng/mL) in the quartile with the greatest percentage of total body fat.¹⁰ In a study by Flancbaum et al., of 379 obese patients (84% women; 25.8% white, 28.4% African American, and 45.8% Hispanic; mean BMI 51.8 kg/m²) presenting for gastric bypass surgery, 68.1% were deficient in 25-hydroxy vitamin D, although levels of vitamin D deficiency were not defined.⁶ In a study by Buffington et al. of 60 obese women presenting for gastric bypass surgery, 62% had vitamin D levels below the normal range defined as 40–185 nmol/L (16–74 ng/mL).¹¹

We found similar rates of deficiency and insufficiency in our group of adults presenting for bariatric surgery. While definitions of deficiency differ from study to study, most acknowledge serum vitamin D is suboptimal at levels below 75 nmol/L (30 ng/mL).⁸ All of our study subjects had some form of vitamin D deficiency or insufficiency, defined as levels below 80 nmol/L (32 ng/mL). As in the NHANES study by Looker et al., black patients had a higher probability of being severely deficient than white patients.¹⁴ This wasn't the case for gender; however, overall, females tended to have higher rates of deficiency than males for all deficiency levels. It is not yet understood why women have a higher prevalence of vitamin D deficiency or insufficiency. And similar to the NHANES study, the deficiency levels among age groups was not statistically different. One limitation of this study is that we did not take into account the seasonality of the blood draw or any vitamin D supplements the patient may be taking. However, the population was from the same latitude (32°N).

The primary source of vitamin D is endogenous production. Cholecalciferol, or vitamin D3, is produced naturally by the skin when exposed to ultraviolet B radiation; thus, serum levels of vitamin D are influenced by length of exposure to UVB radiation, strength of UV according to time of year, latitude (>42°N does not support cutaneous production of vitamin D during the winter), and the use or non-use of sunscreen. Dietary supplements such as calcium supplements and multivitamins typically contain only 400 IU/dose. Fortified foods are limited and contain little vitamin D; vitamin D–fortified milk, for example, provides only 100 IU/cup. Naturally occurring food sources of vitamin D include fatty fish and fish liver oils and, to a lesser extent, shiitake mushrooms and egg yolk.⁸

The Adequate Intake (AI) for vitamin D is 200–600 IU/day for adults > 19 years. The Safe Tolerable Upper Intake Level (UL) set by the Institute of Medicine's Food and Nutrition Board (FNB) at the National Academies in 1997 for vitamin D is 2000 IU; however, the UL has recently been challenged with clinical trial data to demonstrate that vitamin D is not toxic at doses greater than the UL and as high as 10,000 IU/day.¹⁵ The FNB has assembled an expert committee to review recent research on vitamin D and is expected to issue updated Dietary Reference Intakes (DRIs) for vitamin D and calcium in the summer of 2010.

Cutaneous and dietary sources of vitamin D are metabolized by the liver to 25-hydroxyvitamin D, which is the serum marker for determining a patient's vitamin D status.⁸ Optimal serum levels of vitamin D are not yet known, but Bischoff-Ferrari and colleagues suggest serum concentrations for optimizing bone mineral density and fracture reduction risk, improving lower extremity function, and preventing periodontal disease and colorectal cancer require levels > 75 nmol/L (30 ng/mL) and are best between 90 and 100 nmol/L (36–40 ng/mL).⁷ While deficiency is generally defined as <50 nmol/L (20 ng/mL) and insufficiency as 52.5–72.5 nmol/L (21–29 ng/mL), one is considered vitamin D sufficient at serum levels above 75 nmol/L (30 ng/mL), and intoxication occurs at levels >375 nmol/L (150 ng/mL).⁸

Given the limited food and supplement sources of vitamin D, average oral intake is probably inadequate to reach or maintain optimal serum levels. Further, vitamin D absorption is not maximized following a malabsorptive procedure such as the gastric bypass, as it is absorbed like other fatty foods in the jejunum and ileum,¹⁶ which exacerbates the risk of vitamin D deficiency in the post–gastric bypass patient.

A better understanding of the relationship between vitamin D deficiency and the morbidly obese population—specifically, the relationship between vitamin D deficiency and gender, race, BMI, and age—will provide for a better understanding of those who are at risk for vitamin D deficiency post-operatively.

Conclusions

Understanding which characteristics of the morbidly obese population are associated with poor vitamin D status will aid in identifying high-risk groups to allow for adequate repletion of vitamin D before weight reduction surgery. More research is needed to understand why the morbidly obese population in general suffers from vitamin D deficiency and insufficiency and to identify high-risk population groups. In our practice, we have maintained the practice of screening all pre- and post-operative bariatric surgery patients for vitamin D deficiency.

Footnotes

Disclosure Statement

No competing financial interests exist.

References

Hedley

, Ogden

, Johnson

, Carroll

, Curtin

, Flegal

. Prevalence of overweight and obesity among US children, adolescents and adults, 1999–2002. JAMA, 2004; 291:2847–2850.

ASMBS. Bariatric surgery society takes a new name, new mission and new surgery, 2007. www.asbs.org/Newsite07/resources/press_release_8202007.pdf.

Alvarez-Leite

. Nutrient deficiencies secondary to bariatric surgery. Clin Nutr Metab Care, 2004; 7:569–575.

Compher

, Badellino

, Boullata

. Vitamin D and the bariatric surgical patient: a review. Obes Surg, 2008; 18:220–224.

Clements

, Katasani

, Palepu

et al. Incidence of vitamin deficiency after laparoscopic Roux-en-Y gastric bypass in a university hospital setting. Am Surg, 2006; 72:1196–1202.

Flancbaum

, Belsley

, Drake

, Calarusso

, Tayler

. Preoperative nutritional status of patients undergoing Roux-en-Y gastric bypass for morbid obesity. J Gastro Surg, 2006; 10:1033–1037.

Bischoff-Ferrari

, Giovannucci

, Willett

, Dietrich

, Dawson-Hughes

. Estimation of optimal serum concentrations of 25-hydroxyvitamin D for multiple health outcomes. Am J Clin Nutr, 2006; 84:18–28.

Holick

. Vitamin D deficiency. NEJM, 2007; 357:266–281.

Martini

, Wood

. Vitamin D status and the metabolic syndrome. Nutr Rev, 2006; 64:479–486.

10.

Arunabh

, Pollack

, Yeh

, Aloia

. Body fat content and 25-hydroxyvitamin D levels in healthy women. J Clin Endocrinol Metab, 2003; 88:157–161.

11.

Buffington

, Walker

, Cowan

Jr , Scruggs

. Vitamin D deficiency in the morbidly obese. Obes Surg, 1993; 3:421–424.

12.

Ybarra

, Sanchez-Hernandez

, Perez

. Hypovitaminosis D and morbid obesity. Nurs Clinic North Am, 2007; 42:19–27.

13.

Hollis

. Circulating 25-hydroxyvitamin D levels indicative of vitamin D sufficiency: implications for establishing a new effective dietary intake recommendation for vitamin D. J Nutr, 2005; 135:317–322.

14.

Looker

, Dawson-Hughes

, Calvo

, Gunter

, Sahyoun

. Serum 25-hydroxyvitamin D status of adolescents and adults in two seasonal subpopulations from NHANES III. Bone, 2002; 30:771–777.

15.

Hathcock

, Shao

, Vieth

, Heaney

. Risk assessment for vitamin D. Am J Clin Nutr., 2007; 85:6–18.

16.

Jacques

. Micronutrition for the Weight Loss Surgery Patient. Edgemont, PA: Matrix Medical Communications, 2006.