Assessment of vitamin B(6) status in Korean patients with newly diagnosed type 2 diabetes.

Abstract

The purpose of this study was to assess vitamin B(6) intake and status in Korean patients with newly diagnosed type 2 diabetes. Sixty-four patients with newly diagnosed type 2 diabetes and 8-11% glycated hemoglobin (A1C), along with 28 age-matched non-diabetic subjects, participated. Dietary vitamin B(6) intake was estimated by the 24 hour recall method and plasma pyridoxal 5'-phosphate (PLP) was measured. There was a significant difference in daily total calorie intake between the diabetic and non-diabetic groups (1,917 ± 376 vs 2,093 ± 311 kcal). There were no differences in intake of total vitamin B(6) (2.51 ± 0.91 vs 2.53 ± 0.81 mg/d) or vitamin B(6)/1,000 kcal (1.31 ± 0.42 vs 1.20 ± 0.32 mg) between the diabetic and non-diabetic groups, andI intakes of total vitamin B(6) were above the Korean RDA in both groups (180.0 ± 57.9 vs 179.0 ± 65.4). There was a higher percentage of diabetic subjects whose plasma PLP concentration was < 30 nmol/L compared to non-diabetic group. Plasma PLP levels tended to be lower in the diabetic subjects than in the non-diabetic subjects, although the difference was not statistically significant due to a large standard deviation (80.0 ± 61.2 nmol/L vs 68.2 ± 38.5 nmol/L). Nevertheless, plasma PLP levels should be monitored in pre-diabetic patients with diabetic risk factors as well as in newly diagnosed diabetic patients for long-term management of diabetes, even though this factor is not a major risk factor that contributes to the development of degenerative complications in certain patients.

Full text

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Nutrition Research and Practice (Nutr Res Pract) 2011;5(1):34-39
DOI: 10.4162/nrp.2011.5.1.34
Assessment of vitamin B6 status in Korean patients with newly diagnosed type 2 diabetes
Hee Jung Ahn1, Kyung Wan Min1 and Youn-Ok Cho2§
1Department of Internal Medicine, Eulji Medical College, Seoul 139-872, Korea
2Department of Food and Nutrition, Duksung Women's University, 419 Ssangmun-dong, Dobong-gu, Seoul 132-714, Korea
Abstract
The purpose of this study was to assess vitamin B6 intake and status in Korean patients with newly diagnosed type 2 diabetes. Sixty-four patients
with newly diagnosed type 2 diabetes and 8-11% glycated hemoglobin (A1C), along with 28 age-matched non-diabetic subjects, participated. Dietary
vitamin B6 intake was estimated by the 24 hour recall method and plasma pyridoxal 5'-phosphate (PLP) was measured. There was a significant
difference in daily total calorie intake between the diabetic and non-diabetic groups (1,917 ± 376 vs 2,093 ±311 kcal). There were no differences
in intake of total vitamin B6 (2.51 ± 0.91 vs 2.53 ±0.81 mg/d) or vitamin B6/1,000 kcal (1.31 ± 0.42 vs 1.20 ±0.32 mg) between the diabetic and
non-diabetic groups, andI intakes of total vitamin B6 were above the Korean RDA in both groups (180.0 ±57.9 vs 179.0 ±65.4). There was a higher
percentage of diabetic subjects whose plasma PLP concentration was < 30 nmol/L compared to non-diabetic group. Plasma PLP levels tended to
be lower in the diabetic subjects than in the non-diabetic subjects, although the difference was not statistically significant due to a large standard
deviation (80.0 ±61.2 nmol/L vs 68.2 ±38.5 nmol/L). Nevertheless, plasma PLP levels should be monitored in pre-diabetic patients with diabetic
risk factors as well as in newly diagnosed diabetic patients for long-term management of diabetes, even though this factor is not a major risk
factor that contributes to the development of degenerative complications in certain patients.
Key Words: Vitamin B6 intake, vitamin B6 status, plasma pyridoxal 5'-phosphate, type 2 diabetes
Introduction5)
In developed countries, classical vitamin-deficiency syndromes
such as scurvy, beriberi, and pellagra are now uncommon, but
specific population subgrozups remain at risk for modest vitamin
insufficiencies. This is notably the case in diabetes patients who
frequently display inadequate vitamin status, including many
from the B group. Diabetes mellitus is a metabolic disorder
characterized by hyperglycemia and insufficiency of secretion or
action of endogenous insulin. Although the etiology of diabetes
is not well defined, aging is a major factor in the development
and progression of diabetes. Due to functional insufficiency, the
vitamin B6 status of elderly individuals may be subject to higher
variability than that of younger adults who are frequently taken
as references. Moreover, it is reported that plasma PLP level
is affected by age and gender [1].
It has been reported that vitamin B6 may be involved in the
metabolism of carbohydrate. Pyridoxal 5'-phosphate (PLP), the
active form of vitamin B6, acts as an integral part of glycogen
phosphorylase (EC 2.4.1.1.) which catalyzes the breakdown of
glycogen [2]. A deficiency of vitamin B6 is associated with
impaired gluconeogenesis [3] and impaired glucose tolerance [4].
It has also been reported that vitamin B6 deficiency can lead
to a decrease in the level of circulating insulin as well as pancreas
function and relates to increased risk of coronary artery disease
in animal models [5,6]. Thus, proper vitamin B6 status can be
deemed an important factor in the care of type 2 diabetes for
the prevention of degenerative complications. However, there
have been few reports on vitamin B6 status in the Korean elderly
population or in those with diabetes.
Therefore, the aim of the present study was to assess vitamin
B6 status using plasma PLP levels and vitamin B6 intakes of
Korean patients with newly diagnosed type 2 diabetes since
plasma PLP level [7,8] and vitamin B6 intake have been the most
accepted and widely used indices of vitamin B6 status in the
last decade. In addition, these status indices were compared to
those of age and gender-matched healthy non-diabetic subjects
to exclude variance from age, as well as gender effects.
Subjects and Methods
Subjects
Sixty-four patients with newly diagnosed type 2 diabetes and
8-11% glycated hemoglobin (A1C), which is used primarily to
identify average plasma glucose concentrations over a prolonged
period of time, and 28 age-matched healthy non-diabetic subjects
§Corresponding Author: Youn-Ok Cho, Tel. 82-2-901-8376, Fax. 82-2-901-8372, Email. yunokcho@duksung.ac.kr
Received: October 25, 2010, Revised: February 8, 2011, Accepted: February 9, 2011
ⓒ2011 The Korean Nutrition Society and the Korean Society of Community Nutrition
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/)
which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Hee Jung Ahn et al.
35
Category
Non-diabeticDiabetic
Men
(n= 15)
Women
(n= 13)
Total
(n = 28)
Men
(n = 36)
Women
(n = 28)
Total
(n = 64)
Age (yrs)50.6± 12.3 49.5 ± 9.850.0 ± 10.847.9 ± 11.755.4 ± 13.651.5 ± 12.9
Height (cm)167.1 ± 4.6157.0 ± 7.0161.0 ± 7.9170.6 ± 5.9156.3± 6.2164.0± 9.5
68.7± 10.3**3)
Weight (kg)
BMI2)
66.1 ± 8.952.4 ± 8.559.2 ± 11.072.7 ± 10.0 63.7 ± 6.5
23.6 ± 2.621.2 ± 2.6 22.5± 3.124.9± 2.826.1 ± 2.225.5 ± 2.6**
1)Diabetic subjects had newly diagnosed type 2 diabetes with 8-11% A1C and non diabetic subjects were age-matched.
2)BMI; Body mass index = weight(kg)/height(m2)
3)** Significant difference between non-diabetic and diabetic subjects at P < 0.01
Table 1. General characteristics of non-diabetic and diabetic1) subjects
NutrientNon-diabetic (n = 28)Diabetic (n = 64)
2,093± 311*2)
323 ± 56.3ns
91.9± 26.7ns
47.8± 24.0ns
44.1± 11.7ns
52.0± 26.2ns
27.7± 16.9ns
24.3± 16.1ns
267± 196ns
684± 317ns
1,205 ± 357ns
19.0± 5.91ns
5,159± 1,909ns
3,339 ± 923ns
83.6 ± 460ns
1.39± 0.49ns
1.24± 0.38ns
2.53± 0.81ns
19.0± 6.37ns
141 ± 97.7ns
Energy (kcal)1,917 ± 376
Carbohydrate (g)290 ± 43.7
Total protein (g)83.9 ± 19.3
Animal protein (g)39.7 ± 18.7
Plant protein (g)44.1 ± 10.1
Total fat (g)46.2 ± 16.4
Animal fat (g)23.9 ± 15.6
Plant fat (g) 22.3 ± 9.79
Cholesterol (mg)217 ± 131
Calcium (mg)621 ± 227
Phosphorus (mg)1,108 ± 214
Iron (mg)17.0 ± 4.76
Sodium (mg)5,478± 1674
Potassium (mg) 3,236 ± 717
Vitamin A (RE)924 ± 627
Vitamin B1 (mg)
Vitamin B2 (mg)
1.32 ± 0.41
1.24 ± 0.33
Vitamin B6 (mg) 2.51 ± 0.91
Niacin (NE)19.1 ± 6.65
Vitamin C (mg)114 ± 55.3
1)Diabetic subjects had newly diagnosed type 2 diabetes with 8-11% A1C and non
diabetic subjects were age-matched.
2)P-value, ns: not significant at P < 0.05
Table 2. Daily nutrient intakes of non-diabetic and diabetic1) subjects
were recruited consecutively from the diabetes clinic at E
Hospital between February and April, 2005. Subjects were
excluded before recruitment if they were taking supplemental
vitamins, including multivitamins.
Dietary intake and anthropometric measurements
Dietary vitamin B6 intake and food sources were estimated with
the 24 hour recall method. The subjects each reported three
consecutive daily dietary intakes with the help of a trained
interviewer. Food portion sizes were estimated by using standard
household measures and published average portion sizes [9].
Nutrient intakes were estimated using a computer-aided nutritional
analysis program developed by the Korean Nutrition Society [10].
When information was unavailable for a particular food, a value
was assigned based on values for similar foods. The foods in
the vitamin B6 database were categorized into those of animal
or plant origin, and the amount of daily vitamin B6 provided
by these two categories was calculated for each person. On the
day of dietary data collection, weights and heights were measured
and body mass index (BMI) was calculated from the measurements
of body weight and height.
Biochemical and statistical analysis
After a 12-hour fast, venous blood was used for the assessment
of vitamin B6 status and biochemical indices. Immediately
following blood draw into heparinized vacutainers, the blood was
centrifuged at 3,000 rpm for 15 min to separate the plasma. The
plasma was stored at -20℃ in aliquots until analyzed. Plasma
PLP concentration was measured using the HPLC method [11],
which was modified as follows: Mobile phase (0.1 M potassium
dihydrogen phosphate containing 0.1 M sodium perchlorate, 0.5
g/L sodium bisulfite, pH 3) was pumped at a flow rate of 1.0
ml/min into the column (Bondapack ODS column, 3.9×300 mm,
10 μm porus packing, C18, Waters). The plasma was added to
perchloric acid (0.8 M) and allowed to sit for one hour to release
PLP from the protein. This mixture was then centrifuged (18,000
rpm, 4℃, 15 min) and the supernatant removed. One hundred
microliters of supernatant was loaded in the sample loop and
then injected into the column.
Statistical analyses were carried out using the Statistical
Analysis System (SAS). Pearson's correlation coefficient was
used to determine possible relationships among the indices of
vitamin B6 status and blood biochemical indices. Values for
vitamin B6 status were regressed based on vitamin B6 intake and
dietary vitamin B6 to protein ratio.
Results
Because aging is one of the major factors affecting both plasma
PLP levels and the development and progression of diabetes,
comparisons of plasma PLP concentrations of diabetic patients
to those of age-matched healthy non-diabetic subjects are important.
Sixty-four diabetic patients and 28 age-matched non-diabetic
subjects participated in this study, with mean age being 50 years
for the diabetic patients and 51.5 years for the non-diabetic
subjects. The characteristics of the subjects are given in Table
1. Table 2 shows the nutrient intakes of the diabetic patients

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36
Vitamin B6 status in Koreans with type 2 diabetes
Non-diabetic
(n = 28)
Diabetic
(n = 64)
2.53 ± 0.81ns2)
1.20 ± 0.32ns
180.0 ± 57.9ns
69.2 ± 38.5ns
Total vitamin B6 (mg/day)2.51 ± 0.91
Vitamin B6/1,000 kcal (mg)
Percent of Korean RDA (%)1)
1.31 ± 0.42
179.0± 65.4
Mean Plasma PLP (nmol/L) 80.0 ± 61.2
Subjects plasma PLP < 30 nmol/L (%)8.39.7
1)Diabetic subjects had newly diagnosed type 2 diabetes with 8-11% A1C and non
diabetic subjects were age-matched.
2)P-value, ns: not significant at P < 0.05
Table 3. Dietary vitamin B6 intake and plasma PLP levels of non-diabetic and
diabetic1) subjects
Plasma PLP (nmol/L)3)
Non-diabetic (n= 28)
0.033ns2)
0.160ns
-0.125ns
-0.066ns
-0.112ns
Diabetic (n = 64)
0.211ns
0.243ns
-0.138ns
0.075ns
0.048ns
Glucose (mg/dl)
Postprandial glucose (mg/dl)
Triglyceride (mg/dl)
Albumin (g/dl)
Total cholesterol (mg/dl)
1)Diabetic subjects had newly diagnosed type 2 diabetes with 8-11% A1C and non
diabetic subjects were age-matched.
2)P-value, ns: not significant at P < 0.05
3)Plasma pyridoxal 5'-phosphate levels of non-diabetic and diabetic subjects
Table 4. Correlations between plasma PLP level and biochemical values of the
diabetic subjects1)
Vitamin B6 intake (mg/day) Dietary vitamin B6 to protein ratio (mg/g protein)
Fig. 1. Distribution of vitamin B6 intake in non-diabetic and diabetic1) subjects. 1)Diabetic subjects had newly diagnosed type 2 diabetes with 8-11% A1C and non diabetic
subjects were age-matched.
and non-diabetic subjects. There was a significant difference in
daily total calorie intake between the diabetic and non-diabetic
groups (1,917 ±376 vs 2,093±311 kcal/d) due to excess weight
in the diabetic subjects. However, there were no differences in
intakes of other nutrients including vitamin B6. Table 3 shows
dietary vitamin B6 intake and plasma PLP levels for the
non-diabetic and diabetic subjects. There were no differences in
intake of total vitamin B6 (2.51 ± 0.91 vs 2.53 ± 0.81 mg/d) or
vitamin B6/1,000 kcal (1.31 ± 0.42 vs 1.20 ± 0.32 mg) between
the diabetic and non-diabetic groups. The intakes of total vitamin
B6 were above the Korean RDA for both groups. In the diabetic
patients, the mean plasma PLP level was 15% lower as compared
to the non-diabetic subjects (80.0 ±61.2 vs 68.2 ±38.5 nmol/L),
but this difference was not statistically significant due to a large
standard deviation. This indicates that the percentage of diabetic
subjects whose plasma PLP concentration was < 30 nmol/L was
higher than that of the non-diabetic group. Fig. 1 shows the
frequency distribution of daily vitamin B6 intake, and its relative
intake to daily protein intake ratio. Daily vitamin B6 intake was
not normally distributed in either the non-diabetic or diabetic
subjects, and the declination was steeper in the diabetic patients.
Fig. 2 shows there was no significant correlation between plasma
PLP level and intake of vitamin B6 in either the non-diabetic
subjects or diabetic patients. Also, plasma PLP levels and intakes
of vitamin B6 were more widely scattered in the diabetic patients
compared to the non-diabetic subjects. Table 4 shows that no
significant correlations were found between plasma PLP level
and biochemical risk indices including plasma levels of fasting
glucose, postprandial glucose, triglyceride, albumin, and total
cholesterol in either the non-diabetic subjects or diabetic patients.
Discussion
Because there were no differences in total vitamin B6 intake
and vitamin B6/1,000 kcal between the diabetic and non-diabetic
groups, it is considered that the higher energy intake in diabetes
patients did not affect intake of vitamin B6. A possible explanation
for the tendency of lower vitamin B6 status is based on plasma
PLP level, which has been suggested as the best single status
indicator because it appears to reflect tissue stores. In the diabetic
subjects, the mean plasma PLP level was 15% lower than that
of the non-diabetic subjects (80.0 ± 61.2 nmol/L vs 68.2 ± 38.5
nmol/L), but this difference was not statistically significant due
to a large standard deviation.
However, even though there were no differences in total
vitamin B6 intake and vitamin B6/1,000 kcal between the diabetic
and non-diabetic groups, and intakes of total vitamin B6 were
above the Korean RDA in both groups, the percentage of subjects

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Hee Jung Ahn et al.
37
1.001.50 2.00 2.503.00
Daily vitamin B6 intake(mg/day)Daily vitamin B6 intake(mg/day)
Dietary vitamin B6 intake (mg/day)
0.00
50.00
100.00
150.00
200.00
plAM PLP(nmol/l)plAM PLP(nmol/l)
R 제곱 선형 = 0.015

1.002.003.004.005.006.00
Dietary vitamin B6 to protein ratio(mg/g)Dietary vitamin B6 to protein ratio(mg/g)
Dietary vitamin B6 to protein ratio (mg/g)
0.00
50.00
100.00
150.00
200.00
Plasma PLP(nmol/l)Plasma PLP(nmol/l)
1.002.00 3.004.00 5.00
Daily vitamin B6 intake(mg/day) Daily vitamin B6 intake(mg/day)
Dietary vitamin B6 intake (mg/day)
0.00
50.00
100.00
150.00
200.00
Plasma PLP(nmol/l)Plasma PLP(nmol/l)

1.00 2.003.004.005.00
Dietary vitamin B6 to protein ratio(mg/g)Dietary vitamin B6 to protein ratio(mg/g)
Dietary vitamin B6 to protein ratio (mg/g)
0.00
50.00
100.00
150.00
200.00
Plasma PLP(nmol/l)Plasma PLP(nmol/l)
Fig. 2. Scatter plots of plasma PLP levels and vitamin B6 intake in non-diabetic and diabetic1) subjects. 1)Diabetic subjects had newly diagnosed type 2 diabetes with
8-11% A1C and non diabetic subjects were age-matched.
with a plasma PLP concentration < 30 nmol/L (the proposed
cutoff as an index of adequacy in diabetic patients) was higher
in the diabetic subjects as compared to non-diabetic subjects.
Also, plasma PLP levels and intakes of vitamin B6 were more
widely scattered in the non-diabetic group as compared to those
of the diabetic group. Thus, if an eccentric value were considered,
the 15% lower mean plasma PLP level in the diabetic subjects
compared to that of the non-diabetic subjects is thought to be
a meaningful decrease in a clinical situation, although this
difference was not statistically significant. In addition, the results
of this study are consistent with previous studies where circulating
levels of plasma pyridoxal 5'-phosphate and total vitamin B6
significantly decreased under conditions of hyperglycemia [12-14].
However, recent epidemiology of plasma PLP in the U.S.
population showed there was no difference between diabetes and
non-diabetes subjects, regardless of using supplemental vitamin
B6 [15]. This discrepancy may be explained by differences in
major vitamin B6 sources, because several studies have indicated
that the utilization of vitamin B6 from animal derived foods is
more efficient than that from plant foods [16,17]. Furthermore,
it was reported that Koreans obtain approximately 65% of
vitamin B6 from plant sources [18,19], whereas in the American
diet, approximately 50% of dietary vitamin B6 is from meat and
the other 50% is from plant-based foods [20].
There was a previous review on age-associated B vitamin
deficiency as a determinant of chronic diseases [21], and
estimations of how much vitamin B6 is required in diabetes must
take into account all potential age-related alterations. By the
comparison of vitamin B6 status in diabetic patients to that of
age-matched healthy non-diabetic subjects in this study, the
tendency for a lower plasma PLP level in diabetic patients might
not be due to age-related alterations.
This lowered level of plasma PLP in diabetic patients may
be due to either lower intake of vitamin B6 or altered distribution
of PLP in diabetic patients. B vitamin intake is dependent on
the food supply and many studies have demonstrated that
Non-diabeticNon-diabetic
DiabeticDiabetic

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38
Vitamin B6 status in Koreans with type 2 diabetes
increased protein intake causes a relative decrease in B6 status,
as judged by a variety of B6 status indicators [22-24]. Furthermore,
in this study, vitamin B6 intake was highly correlated to intakes
of energy and protein. This has led some to define B6 require-
ments in terms of protein intake or energy intake. However, there
was no difference in vitamin B6 intake when expressed as either
a ratio of vitamin B6 intake to daily protein intake or as the
amount of vitamin B6 intake to a 1,000 calorie intake in this
study. These data show that plasma PLP levels tended to be lower
in the diabetic subjects than in the non-diabetic subjects although
there was no difference in vitamin B6 intake. Thus, in this study,
the lower plasma PLP levels of the diabetic patients might not
have been due to insufficient intake of vitamin B6, but instead
might be due to altered distribution of PLP in diabetic patients.
The mechanism involved in altered distribution of PLP in
diabetes could be that elevated plasma glucose reduces plasma
PLP levels and xanthurenic acid excretion due to abnormal
tryptophan metabolism; xanthurenic acid forms xanthurenic
acid-insulin complexes that reduce insulin sensitivity and result
in elevated blood glucose levels [25]. Decreases of mitochondria
pyridoxal phosphate and aspartate aminotransferase have been
observed in diabetic animals [26]. It was also reported that urinary
excretions of 3-hydroxykynurenine and 3-hydroxyanthranilic acid
were increased in diabetic animals, and this might lead to the
inhibition of islet insulin secretion [27].
In clinical situations, the question still remains whether altered
distribution of PLP contributes to the development of degenerative
complications, or results from those complications. Because no
significant correlations were found between plasma PLP levels
and any of the biochemical risk indices of degenerative diabetes
complications, such as plasma levels of fasting glucose, postprandial
glucose, triglyceride, albumin, and total cholesterol, in either the
non-diabetic or diabetic subjects of this study, the cause-effect
nature of this relationship could not be clarified. However,
considering the major complications that occur in diabetic
patients, maintaining normal vitamin B6 status is an important
diet strategy for diabetic patients since retrospective studies have
suggested the association between risk of cardiovascular disease
and vitamin B6 status, although the cause-effect nature of this
relationship has not been clarified [28-31]. Prospective studies
also suggest that populations with higher PLP concentrations
have lower risk of coronary heart disease [32,33].
Therefore, despite the many uncertainties regarding the mode
of action, these results suggest that plasma PLP levels should
be monitored in pre-diabetic patients with diabetic risk factors
and in newly diagnosed diabetic patients for long-term management
of diabetes, even though this factor is not a major risk factor
that contributes to the development of degenerative complications
in certain patients. The principal limitations of this study were
the cross-sectional design and that a causative nature of the
association could not be established.
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