Wednesday, December 30, 2015

Diabetes Epidemic & You: Part 2

Insulin Patterns During the Oral Glucose Tolerance Test

Dr. Kraft discerned 5 patterns of insulin levels from those 14,384 oral glucose tolerance tests.  Pattern 1 is considered to be a normal insulin response (euinsulinemia), patterns 2, 3 and 4 are considered to be high insulin responses (hyperinsulinemia) and pattern 5 is considered to be a low insulin response (hypoinsulinemia).  These patterns are presented in the graph below


Another measure of the patterns that Dr. Kraft used was the sum of the insulin levels at 2 and 3 hours, which shows a substantial difference between each pattern


Pattern 1
Pattern 2
Pattern 3
Pattern 4
Pattern 5
2h +3h Insulin
43
126
213
320
25

The following table lists the percentage of people in each glucose tolerance and insulin pattern category


NGT (%)
IGT (%)
T2D (%)
TOTAL (%)
Pattern 1
14.7
0.6
0.2
15.5
Pattern 2
29.4
5.2
1.2
35.7
Pattern 3
16.0
11.2
9.3
36.5
Pattern 4
4.0
1.9
2.3
8.2
Pattern 5
2.7
0.4
1.1
4.2
TOTAL
66.7
19.3
14.0


And this table lists the percentage of individuals with normal, impaired and diabetic glucose tolerance for each pattern of insulin levels during the oral glucose tolerance test


NGT (%)
IGT (%)
T2D (%)
Pattern 1
95.0
3.7
1.3
Pattern 2
82.2
14.6
3.2
Pattern 3
43.9
30.7
25.4
Pattern 4
48.8
23.5
27.7
Pattern 5
64.3
9.2
26.5

Interestingly a large number of people with normal glucose tolerance have some degree of hyperinsulinemia, and so the percentage of people with both normal glucose tolerance and insulin levels is staggering small at just 14.7% (or 17.4% if people with NGT and pattern 5 are also included)

Perhaps this is argument that Dr. Kraft inappropriately considered pattern 2 as hyperinsulinemia, whereas it may simply be the upper end of normal.  But this argument – that pattern 2 should also be considered normal – largely depends on an assumption that most of the population is healthy and not on the path to developing disease.  In defence of Dr. Kraft’s classifications, it’s worth pointing out that pattern 1 is almost exclusively the domain of normal glucose tolerance.  Whereas pattern 2 and especially pattern 3 show some overlap with impaired and diabetic glucose tolerance.  The people with normal glucose tolerance and hyperinsulinemia may represent those people who will go onto develop impaired glucose tolerance or type 2 diabetes in the future or are the lucky ones who have a robust pancreas.  However, insulin resistance per se (even without higher glucose levels) isn’t particularly desirable (more on that later)

Lastly while glucose tolerance isn’t a perfect indicator of someone’s insulin levels, I want to also mention that there isn’t often much relationship between fasting glucose and insulin pattern.  The following table lists the fasting glucose levels (average ± SD) by glucose tolerance and insulin pattern.  In summary fasting glucose appears to be an almost completely useless indicator of insulin pattern if the person is not diabetic, but is a good indicator that someone with very severe diabetes has low insulin levels (busted pancreas) 


Pattern 1
Pattern 2
Pattern 3
Pattern 4
Pattern 5
T2D
118 ± 71
126 ± 45
125 ± 45
140 ± 54
240 ± 100
IGT
96 ± 14
97 ± 14
97 ± 14
102 ± 13
102 ± 16
NGT
86 ± 11
85 ± 11
85 ± 11
89 ± 12
84 ± 11

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