Surgical Science, 2013, 4, 547-553
Published Online December 2013 (http://www.scirp.org/journal/ss)
Open Access SS
Complications, Mineral and Vitamin Deficiencies:
Comparison between Roux-en-Y Gastric Bypass
and Sleeve Gastrectomy*
Nina Sauer1#, Jan Wienecke1, Clarissa Schulze zur Wiesfch1, Stefan Wolter2,
Oliver Mann2, Jens Aberle1
1Department for Endocrinology and Diabetology, University Hospital Hamburg Eppendorf (UKE),
2Department for Visceral and Abdominal Surgery, University Hospital Hamburg Eppendorf (UKE),
Received October 22, 2013; revised November 20, 2013; accepted November 28, 2013
Copyright © 2013 Nina Sauer et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Objective: Nutritional deficiencies are known side-effects of bariatric surgeries, specifically in those that bypass the
proximal intestine. Therefore, in clinical practice, vitamin and mineral supplementations are often necessary after such
operations. It was our intention to evaluate, whether alimentary deficiencies occur with the same frequency in patients
following Sleeve-Gastrectomy (SG) compared to Roux-en-Y Gastric Bypass (RYGB) surgeries. Methods: We con-
ducted a retrospective data analysis of 171 patients (121 RYGB, 50 SG). Vitamin levels were compared between SG
and RYGB patients over the first post-operative year. Furthermore, regression analysis was performed with regard to
vitamin and iron supplementations and their recommended dosages. Complications occurring within the first post-sur-
gical year were documented as well. Results: Other than vitamin B6 deficiency, which was found to be more frequent
in SG patients, there was no other significant difference regarding the type of operation and the number of patients who
had these deficiencies. There was no significant difference in average vitamin and iron levels between RYGB and SG.
A minimum dose of 1000 IU vitamin D per day was necessary to affect vitamin D levels. The intramuscular administra-
tion of vitamin B12 was the only route found to be effective. Complications within the first year were rare. Conclusions:
Against common assumptions, vitamin and iron deficiencies in SG patients are not less frequent in the first post-surgi-
cal year in comparison to RYGB patients. Standard supplementations should include iron in premenopausal women:
Vitamin D at least 1000 IU per day and vitamin B12 i.m. administration in case of a deficiency.
Keywords: Nutritional Deficiencies; Vitamin Supplementation; Bariatric Surgery
Bariatric surgeries are considered to be low risk com-
plications. However, vitamin and iron deficiencies occur
more frequently in patients with time after bariatric sur-
gery. The impact of the type of surgery on these deficien-
cies in former studies has been controversial. In Roux-
en-Y Gastric Bypass (RYGB), a small stomach pouch is
created. The small intestine is separated by the distal liga-
ment of Treitz and the distal intestines are connected by
anastomosis with the stomach pouch. The pancreaticobi-
liary limb is joined approximately by 100 - 250 cm distal
of the stomach pouch thereby causing nutrition to bypass
the proximal intestines. On the contrary, in Sleeve Gas-
trectomy (SG), mostly the gastric volume is decreased,
therefore, nutritional deficiencies are mainly expected in
RYGB. In our study, we have investigated a group of
obese patients (n = 171) undergoing the two most com-
mon types of bariatric surgeries (RYGB or SG), with
regard to the prevalence of iron and vitamin deficien-
cies one year after the procedure, as well as the post-
surgical complication rates in our patients.
2. Patients and Methods
*The authors declare no conflict of interest. Informed consent was
obtained from all patients.
#Corresponding author. Data was collected retrospectively from patients who had
N. SAUER ET AL.
undergone either RYGB or SG and had attended our in-
terdisciplinary obesity outpatient clinic for follow-up
between September 2010 and September 2011 (n = 330).
Patients who underwent two bariatric operations during
the follow up period (such as the conversion from SG
into RYBG) were excluded (n = 6).
To provide reasonable comparability between the
cases, patients who did not attend the outpatient clinic
postoperatively between months 10 and 14 were also
excluded from the analysis (n = 153). If a patient at-
tended the clinic more than once during this time interval,
the visit closest to surgery was chosen. However, follow-
up visits were recommended to both groups in the fol-
lowing periods: 3, 6, 9, 12, 18 and 24 months postopera-
tive, followed by yearly visits for life-time.
A population of 171 patients were examined concern-
ing baseline data, complications of surgery, and vitamin
and iron deficiencies. Data was collected using electronic
patient files. Vitamins and iron deficiencies were defined
according to the normal range provided by the clinical
laboratory of our hospital: Iron deficiency = Ferritin < 22
µg/l, vitamin B12 deficiency = vitamin B12 < 197 ng/l,
vitamin D deficiency = 25(OH)D3 < 20 µg/l, vitamin B1
deficiency = vitamin B1 < 80 nMol/l, vitamin B6 defi-
ciency = vitamin B6 < 7.5 µg/l.
Our standard supplementation recommendations in-
cluded the following: Primary prevention with multi-
vitamin supplementations 1 - 2 tablets per day (each tab-
let containing 2.5 µg vitamin B12) and 1g calcium citrate
per day. If a deficiency was present then the following
doses were given for the concerned deficient element:
Vitamin B12 was given as intramuscular (i.m.) injection
of 1000 µg per months, vitamin D 20,000 IU orally (p.o.)
per week, vitamin B6 10 mg p.o. per day, vitamin B1 100
mg p.o. per day and 180 mg iron-sulphate-complex p.o.
For all statistical tests a p < 0.05 was considered statis-
tically significant. Data collection was performed on Mi-
crosoft Excel 2007. Statistical analysis was performed
using Statistical Package of the Social Sciences (SPSS)
19.0. The statistical analysis was performed according to
the recommendations of a biostatistician.
Average vitamin and iron levels in the two groups with
different types of surgeries were tested using t-tests, the
number of patients with deficiencies in both groups using
chi-square tests. Testing for independent variables of
vitamin and iron deficiencies were performed using lin-
ear regression models of SPSS (Figure 1).
Patient characteristics are presented in Table 1. The body
Figure 1. Frequencies of iron and vitamin deficiencies and complications rate within the first postoperative year. (Abbrevia-
tions: Pulm. Embolism = Pulmonary Embolism, Insuf. of Anastomosis = Insufficiency of Anastomosis, Suture Insuf. = Sutur e
Insufficiency, Vit. B6 = Vitamin B6, Vit. B1 = Vitamin B1, Vit. D = Vitamin D, Vit. B12 = Vitamin B12)
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N. SAUER ET AL. 549
Table 1. Baseline patient characteristics and reduction of
BMI after 1 year; (Abbreviations: BMI = Bod y Mass Index,
RYGB = Roux-en-Y Gastric Bypass, SG = Sleeve Gastrec-
tomy); The values for “Age”, “BMI preoperative”, and
“BMI at year 1” are listed as “mean ± standard deviation”.
Age (years) 43.62 ± 10.66
BMI preoperative (kg/m2) 51.26 ± 8.55
BMI at year 1 (kg/m2) 35.38 ± 7.48
Type of surgery
mass index (BMI) reduced significantly from 51.3 kg/m2
to 35.4 kg/m2 (p < 0.05). The majority of patients (80%)
were female and about 70 percent of patients obtained a
There were significantly more male patients in the
group treated with SG (male: 30%, female: 70%) com-
pared to those with RYGB (male: 11.6%, female 88.4%).
Pre- and post-operative mean BMI was higher in pa-
tients with SG in comparison to those with RYGB
(RYGB-BMI-decrease: 48.8 ± 7.1 kg/m2 - >33.0 ± 6.0
kg/m2; SG-BMI-decrease: 55.8 ± 9.2 kg/m2 - > 41.3 ± 7.6
kg/m2). Both groups did not show a statistically signifi-
cant difference in age (42.8 ± 10.4 years RYGB vs. 45.5
± 11.2 years SG).
Iron and vitamin deficiencies, as well as average vita-
min levels and further complications within the first post-
operative year are presented in Table 2 and graph 1. Iron
deficiency was the most frequent to occur after the first
post-operative year (22.9%). Other than vitamin B6 defi-
ciency, which was found to be more frequent in SG pa-
tients, there was no other significant difference regarding
the type of operation and the number of patients who had
these deficiencies. In addition, there was no significant
difference in average vitamin and iron levels between
RYGB and SG.
Hair loss was the most frequent complication and oc-
curred in about two thirds of all cases within the first
post-operative year. However, the frequency differed
significantly between the different types of surgeries (p <
0.05). About 75% of RYGB-patients reported hair loss,
whereas only 50% of SG-patients did. All other compli-
cations were rare, and statistical significance between the
two groups was not reached (graph 1).
Additionally, we investigated the influence of alimen-
tary supplementations as well as the influence of type of
surgery on iron and vitamin levels one year after the op-
eration by regression analysis (Table 3). The type of
surgery had no influence on any of the deficiencies.
However, ferritin levels were related to age, sex and iron
supplementations (p < 0.05). Lack of vitamin B1 and B6
were not related to supplementations, while vitamin B1
significantly correlated with age. However, 25(OH)D3
levels showed a clear positive association with vitamin D
supplementations and this was dose-dependent. At least
1000 IU of vitamin D per day were necessary to show a
significant effect on vitamin D levels. This association
was even higher if replaced with 20,000 IU per week.
However, 400 - 600 IU of vitamin D were found not to
be sufficient to prevent vitamin-D deficiency. A similar
association was found for vitamin B12. Only the intra-
muscular route supplementation of vitamin B12 was
found to have a significant effect on improving vitamin
RYGB and SG are both considered effective and safe
treatments for obesity .
Nutritional deficiencies are common in the post-op-
erative phase of such surgeries and are often not consid-
ered as complications, but rather as expected side-effects
. The Clinical Practice Guidelines of the Endocrine
Society suggest long term mineral and vitamin supple-
mentations in all patients undergoing bariatric surgery
with detailed recommendations for all affected vitamins
. Relation of sex and age in regression models for fer-
ritin, as seen in our patients as well, is likely to be due to
lower ferritin levels in young pre-menopausal women.
The prevalence is about 30%. Therefore, in addition to
multi-vitamin supplementations, general prophylactic
iron substitution should be recommended in all pre-
menopausal women after bariatric surgeries [4,5]. De-
spite a statistically significant higher rate of men in the
group with SG, there was neither a significantly higher
percentage of patients with iron deficiency in the RYGB
group, nor a significantly higher mean iron level in the
SG group. This finding supports the thesis that, against
common assumptions, RYGB does not lead to iron defi-
ciency more frequently.
Recent data suggests that vitamin B12 deficiency is a
common complication after RYGB with a prevalence
between 8% and 80% [6-10]. Optimal supplementation
dosage and type of supplementation has not been inve-
stigated in depth . Our data illustrated that oral sub-
stitution of doses included in conventional multivita-
min tablets (in our study 2.5 µg one to two times per day)
did not have a significant effect on vitamin B12 levels,
whereas, intramuscular vitamin B12 supplementation
correlated with a significant increase in vitamin B12 lev-
According to our clinical experience, there is poor pa-
tient compliance with additional oral vitamin B12 doses.
Therefore our recommendation for vitamin-B12-deficient
patients is the monthly intramuscular dose. Whether oral
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N. SAUER ET AL.
Table 2. Iron, vitamin deficiencies and complications within the first post-operative year; (Abbreviations: RYGB = Roux-en-
Y Gastric Bypass, SG = Sleeve Gastrectomy).
Total RYGB SG Chi-Square
Alimentary Deficiencies n % n % n % p
Iron 39 22.9% 29 24.0% 10 20.4% 0.617
Vitamin B12 7 4.1% 6 5.0% 1 2.0% 0.386
Vitamin D 19 18.1% 13 19.4% 6 15.8% 0.644
Vitamin B1 0 0.0% 0 0.0% 0 0.0% n.s.
Vitamin B6 26 16.9% 13 11.9% 13 28.9% 0.011*
Dumping Syndrom 3 1.8% 2 1.7% 1 2.0% 0.862
Suture Insufficiency 1 0.6% 0 0.0% 1 2.0% 0.115
Thrombosis 4 2.4% 4 3.3% 0 0.0% 0.198
Pulmonary em bolism 1 0.6% 1 0.8% 0 0.0% 0.523
Abdominal hernia 10 5.9% 6 5.0% 4 8.2% 0.421
Gallstones 3 1.8% 3 2.5% 0 0.0% 0.266
Loss of hair 107 66.9% 84 75.0% 23 47.9% 0.001*
supplementation with vitamin B12 in the dose of 350
µg/day is able to increase its levels (as recommended by
The Endocrine Society with strict compliance) was not
investigated in our data.
According to the current literature, vitamin B1 defi-
ciency can occur within the first year after bariatric sur-
gery and can lead to severe neurological consequences
[11-14]. However, none of our patients developed thia-
mine deficiency in the first postoperative year. This
finding is consistent with a prospective study about nutri-
tional deficiencies in SG compared to RYGB surgeries.
The authors did not find vitamin B1 deficiencies in either
group (n = 136 patients), up to 36 months after surgery
. According to The Endocrine Society Clinical Prac-
tice Guidelines, supplementations should be administered
parenterally once neurologically symptomatic. However,
as early recognition is necessary to avoid complications,
for example, caused by dextrose infusion, one should
consider thiamine deficiency especially in case of post-
operative vomiting and initiate appropriate treatment
In addition, despite being substituted with ten times
the dosage of the recommended oral vitamin B1 intake,
none of our patients had significantly higher vitamin B1
levels. The same was observed regarding vitamin B6
Vitamin D deficiency is common in obese patients and
might lead to diseases such as osteoporosis and its asso-
ciated complications . However, our data confirmed
that daily supplementation with at least 1000 IU vitamin
D or even weekly supplementation with 20,000 IU has a
significant positive effect on vitamin D levels. Patients
who substituted other formulas of vitamin D, with a
lower daily dosage did not show significantly higher vi-
tamin D levels. This should encourage therapists to en-
sure that patients take at least the recommended daily
dosage of 1000 IU in order to increase the levels or pre-
vent vitamin D deficiency.
Preoperative nutritional deficiencies are common in
morbidly obese patients .
In a randomized clinical trial that compared SG to
RYGB nutritional deficiencies occurred at the same rate
in both groups except for vitamin B12 deficiency which
was more common after RYGB . There was even
data pointing towards a positive effect of SG as well as
RYGB on the post-operative increase of vitamin D levels
In a recent study, one clear comparison between pre-
and post-operative nutritional status between SG and
RYGB was performed . The referred study showed,
consistent with our results, that post-operative vitamin
D3-deficiency was frequent in both groups, but signifi-
cantly more in RYGB, which was not the case in our
results. Equally to our investigations, there was no pa-
tient suffering from vitamin B1 deficiency. Vitamin B6
deficiency was frequent in our patients on the contrary to
the referred analysis. Our data illustrated that after one
year vitamin B12 deficiency was not found to be frequent,
however, it was quite common in the patients investi-
gated by Gehrer et al. The rate of vitamin D-deficiency
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N. SAUER ET AL. 551
Table 3. Regression analysis of nutritional substitution and type of surgery (Abbreviations: RYGB = Roux-en-Y Gastric By-
pass, SG = Sleeve Gastrectomy, y = year, fem. = female)
Ferritin Vitamin B1 Vitamin B6
coefficient B sig regression
coefficient Bsig regression
Age (y) 1.530 0.002 Age (y) 1.215 0.026Age (y) 0.044 0.767
Sex (fem./male) 88.560 0.000
Sex (fem./male) 2.742 0.858Sex (fem./male) −6.340 0.135
Type of surgery
(RYGB/Sleeve) 4.415 0.708
Type of surgery
(RYGB/Sleeve) −8.398 0.519Type of surgery
(RYGB/Sleeve) −4.205 0.235
Substitution of iron
(no/yes) −44.687 0.000
25 (OH) D3 Vitamin B12
coefficient B sig regression
Age (y) 0.039 0.711 Age (y) 0.971 0.726
Sex (fem./male) −1.883 0.560
Sex (fem./male) −93.461 0.244
Type of surgery
(RYGB/Sleeve) −0.547 0.825
Type of surgery
(RYGB/Sleeve) −3.914 0.953
IE/week (no/yes) 12.487 0.000
Vitamin B12 i.m.
(no/yes) 298.027 0.000
Colecalciferol 500 -
1000 IE/d (no/yes) 10.416 0.019
Vitamin B12 oral
(no/yes) 138.136 0.281
Substitution of other
type of Vitamin D
(no/yes) 6.876 0.440
was statistically higher in post-operative patients with
RYGB compared to SG in the referred study, however,
that was not established in our data.
Further comparisons exist regarding malnutritional
differences between RYGB and biliopancreatic diversion
. Since the need for life-long supplementations after
RYGB is a frequent concern before bariatric surgery, SG
should not be recommended over RYGB with the inten-
tion of preventing malnutrition according to our data. A
study comparing vitamin D levels between both types of
surgical interventions showed that pre- and post-inter-
ventional mean 25-OH-D3-levels were within normal
range in both groups, while showing significant increase
of levels after surgery only in SG-patients . These
findings, against our results, point towards an advantage
of SG concerning vitamin D and therefore, bone metabo-
lism in comparison to RYGB.
The overall complication rate was low in the cohort
study. Complications directly related to the surgical in-
tervention occurred in less than 1% of patients. No sig-
nificant association was found between complication rate
and type of surgery, except for hair loss. Hair loss was
significantly greater among patients undergoing RYGB
than SG-patients. This might be most likely due to more
significant effect of telogen effluvium with RYGB given
added stress of higher rate of weight loss and more inva-
sive procedure of RYGB vs. SG.
Post-operative gallbladder stones were seen with a
lower frequency than in the average population. Since
symptomatic gallbladder stone formation is generally a
problem during weight loss and as previous studies
showed a much higher incidence rate, we assume that our
observation is mainly due to the prophylactic use of ur-
sodeoxycholic acid (UDCA, 500 mg/day) in all patients
for at least 6 months following surgery. Up to our know-
ledge, there is only one publication comparing the use of
UDCA following bariatric surgery prospectively .
Our data confirmed the observation of Miller et al., and
we therefore, strongly recommend the prophylactic use
of UDCA in all bariatric patients for a minimum postop-
erative period of 6 months.
Due to the loss of pyloric control, dumping is mainly
considered to be a complication of RYGB. However,
after SG gastrointestinal motility might be altered and re-
gular transit of food into the duodenum can be impaired.
Interestingly in our study, the prevalence of postopera-
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N. SAUER ET AL.
tive dumping was not different between RYGB and SG.
Recent data showed that late dumping scores increased
gradually with time up to 12 months after SG, as well as
hypoglycaemia . Further data report postprandial
hyperinsulinemic hypoglycaemia in some cases up to 2
years after surgery . Therefore, it is possible that
other long-term complications can occur, but are not
emphasized in our analysis, as our data were collected
for one year following the bariatric surgery.
Against common assumptions, vitamin and iron deficien-
cies in SG patients are not less frequent in the first post-
surgical year in comparison to RYGB patients. Standard
supplementations should include iron in premenopausal
women: Vitamin D at least 1000 IU per day and vitamin
B12 i.m. administration in case of a deficiency. Regular
oral intakes of vitamin B1 and B6 in addition to routine
multi-vitamin supplementations were found to be inef-
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