In the news: Coffee & Type 2 Diabetes Risk, Ocular Blood Flow in Glaucoma Patients with Diabetes

Ocular Blood Flow in Diabetics with OAG

Some research suggests that people with diabetes are more likely to develop glaucoma than are non-diabetics, and that the likelihood of developing diabetes is higher in those with open angle glaucoma (OAG). Other studies have not observed these associations. While the relationship between glaucoma and diabetes remains unclear, vascular complications are common to both.

Autoregulation is the ability of vascular beds to maintain relatively constant blood flow despite changes in pressure, while meeting the metabolic needs of the tissue. Numerous studies suggest that glaucoma patients have impaired autoregulation in vascular systems of the eye. Likewise, diabetic patients have been shown to exhibit impaired vascular regulation. These defects can lead to ischemic damage of the optic nerve head (ONH).

Researchers at Indiana University recently evaluated the impact of retinal blood flow on ONH structure (morphology) in 66 OAG patients with and without diabetes (1). Changes in retinal capillary blood flow, assessed at baseline and at 3 years, were more strongly correlated with detrimental changes in ONH morphology in diabetic patients – results suggesting that OAG patients with coexisting diabetes may be more sensitive to abnormal retinal blood flow.

Coffee May Lower Risk of Type 2 Diabetes

According to the American Diabetes Association (ADA), 25.8 million Americans have diabetes (mostly type 2), while 79 million aged 20 and older have prediabetes. Increased physical activity and healthy weight maintenance are considered cornerstones of type 2 prevention. It may be that drinking coffee confers some protective benefit as well.

The results of prospective cohort studies suggest that long-term caffeinated coffee consumption is associated with type 2 diabetes risk reduction. To further test this association, researchers from the Harvard School of Public health examined the associations between 4-year changes in coffee consumption and risk of type 2 in the following 4 years.2 The researchers prospectively followed over 123,700 men and women. At the end of follow-up, 7,269 cases of incident type 2 diabetes were documented.

People who increased their consumption of caffeinated coffee by more than a cup per day had an 11% lower risk of type 2 diabetes compared with those whose consumption held steady, while decreasing coffee intake by more than a cup a day was linked to a 17% increased risk. These changes in risk were independent of initial coffee intake and 4-year changes in other dietary and lifestyle factors.
 
‘Decaf or Regular’? How Much Coffee Daily?
 
No changes in risk were seen for decaffeinated coffee drinkers in this study. However consumption was low and only a small portion of ‘decaf’ drinkers made substantial changes in their intake. Many other studies have linked higher intake of both caffeinated and decaf with a lower risk for type (2).
 
How much coffee may be of benefit? Previous studies suggest that up to 6 cups daily may lower risk, and that coffee is associated with risk reduction in a dose response manner. A recent review of prospective studies found 9% and 6% risk reductions for each additional daily cup of caffeinated and decaf coffee, respectively (3).
 
Older people with high blood pressure should check with their physician about caffeine consumption. However, a review and meta-analysis found no association between long-term coffee consumption and increased blood pressure or between habitual coffee intake and an increased risk of CVD in hypertensives (4).

References

1. Lee E, et al. The influence of retinal blood flow on open-angle glaucoma in patients with and without diabetes. Eur J Ophthalmol Dec, 2013. [Epub ahead of print]
2. Bhupathiraiu SN, et al. Changes in coffee intake and subsequent risk of type 2 diabetes: three large cohorts of US men and women. Diabetologia [Epub Apr 2014]
3. Ding M, et al. Caffeinated and decaffeinated coffee consumption and risk of type 2 diabetes: a systematic review and a dose-response meta-analysis. Diab Care 37:569–86, 2014.
4. Mesas AE, et al. The effect of coffee on blood pressure and CVD in hypertensive individuals: a systematic review and meta-analysis. Am J Clin Nutr 94:1113-26, 2011.