NEW YORK (Reuters Health) – In type 2 diabetics with multiple comorbidities, tight glycemic control does not provide the same cardiovascular benefits that it does in diabetics with fewer diseases, new research suggests.
In the December 15 Annals of Internal Medicine, the investigators note that post hoc analyses of earlier large trials suggested that only younger diabetics and those without heart disease had any cardiovascular benefit from maintaining relatively normal hemoglobin (Hb)A1c levels.
“We have been aware for some years, and therefore studying, the powerful potential role of comorbidity in diabetes,” lead author Dr. Sheldon Greenfield told Reuters Health. “We wanted to see whether, if we had a really good measure of comorbidity, what the real quantitative impact was.”
“Even we were surprised at the magnitude of the impact on long term outcomes,” he added.
In their article, Dr. Greenfield, from the Health Policy Research Institute in Irvine, California, and his colleagues report on a 5-year (1999 to 2004) longitudinal study of 2613 patients in Italy with type 2 diabetes. Patients with Total Illness Burden Index (TIBI) scores less than 12 were classified as having low to moderate comorbidity (n = 1498), and those with scores or 12 or higher as having high comorbidity (n = 1115).
The main outcome measure was incident cardiovascular events over 5 years, which included angina, myocardial infarction, stroke, transient ischemic attack, coronary revascularization procedures, lower limb complications, and cardiovascular mortality.
Overall, there were 207 cardiovascular events in the low-to-moderate comorbidity group and 219 in the high comorbidity group. Corresponding survival rates at 5 years were 94.2% and 89.9%.
In the healthier group, an HBA1c of 6.5% or less at baseline was associated with a lower rate of incident cardiovascular events (2.2 vs 3.8 events per 100 patient-years, adjusted HR 0.60, p = 0.005).
On the other hand, in the group with higher TIBI scores, there was no significant difference in cardiovascular event rates with baseline HBA1c levels above or below 6.5% (4.9 vs 5.2 events per 100 patient-years, adjusted HR 0.92, p = NS).
The pattern was similar when the baseline HbA1c cutoff was 7.0% or less.
According to Dr. Greenfield, “The strength of our TIBI approach is that it adds up all the conditions, heart disease and everything else, and it is the interaction and sum of these, rather than one major condition, that appears to make the difference.
The authors conclude that their findings support tight glycemic control for younger patients with fewer comorbidities and less stringent HbA1c goals for patients with many complications and comorbid conditions.
Dr. Greenfield recommends an HbA1c target of between 8% and 7% for patients with high comorbidities. “For those with no or very little comorbidity, shoot for less than 7%. That is consistent across this and many prior studies.”
This study was funded with a grant from Pfizer of Italy.
Reference:
Ann Intern Med 2009;151:854-860.
