A new study published in the journal Diabetology & Metabolic Syndrome discovered that low vitamin D levels were associated with an increased risk for premature mortality in men with type 2 diabetes. The study also found that high levels of parathyroid hormone were associated with an increased risk for premature mortality in women with type 2 diabetes.
Diabetes is the seventh leading cause of death in the U.S., responsible for over 75,000 deaths each year. Approximately 29.1 million people in the U.S. have diabetes with type 2 diabetes accounting for about 90 to 95 percent of the cases in adults
Type 2 diabetes is a chronic condition, in which the body resists the effects of insulin or doesn’t produce adequate amounts of insulin to maintain a normal blood sugar level. Insulin is a hormone made by pancreatic beta cells that regulates the body’s blood sugar level. If the bloodstream has too much sugar, insulin helps store the sugar in the liver. If the bloodstream is low in sugar or needs more sugar, insulin releases the sugar from the liver. Insulin also allows your cells to absorb sugar from the bloodstream for energy.
Studies have shown a link between vitamin D and type 2 diabetes. Vitamin D may help the pancreatic beta cells function better and increase the body’s sensitivity to insulin.
Researchers recently conducted a study to assess whether vitamin D status is an independent risk factor for mortality among patients with type 2 diabetes. They enrolled 698 patients who participated in a community-based cohort, Cardiovascular Risk factors in Patients with Diabetes (CARDIPP). All patients had type 2 diabetes and were between the ages of 55 and 66 years old when they were recruited from health care centers in Sweden. The researchers enrolled an additional 129 age-matched controls from the Cardiovascular Reference Population (CAREFUL).
The researchers followed the patients with type 2 diabetes for about six years. They wanted to find out whether there was a relationship between baseline vitamin D status and mortality. The researchers determined mortality with the Swedish Cause of Death Registry.
Additionally, the researchers assessed whether vitamin D status could be used as a predictor of prognosis for type 2 diabetes, independent of regularly used predictors. The major cause of death in type 2 diabetes is cardiovascular disease. Therefore, the researchers used ultrasound markers of cardiovascular disease: the aortic pulse wave velocity (PWV) and the thickness of the intima and media (IMT) of carotid arteries.
Aortic pulse wave velocity is a marker of aortic stiffness, and may be easily measured by using noninvasive ultrasound methods. Intima-media thickness measures the two innermost layers of an artery by ultrasound. IMT detects the presence of atherosclerosis, or the buildup of plaque in the arteries.
Did patients with type 2 diabetes have lower vitamin D levels than the non-diabetic controls? Was vitamin D status associated with mortality independently of PWV and IMT? Here is what the researchers found:
- Patients with type 2 diabetes had significantly lower levels of vitamin D. This relationship remained significant after adjustment for age, gender and BMI (p < 0.01).
- Vitamin D levels didn’t significantly correlate with PWV (p = 0.07) or IMT (p = 0.83).
- After adjusting for potential confounding factors, such as age, waist circumference, blood pressure, PWV and carotid IMT, low vitamin D status was significantly related to an increased risk of mortality in men with type 2 diabetes (p = 0.028).
- After adjusting for the same potential confounding factors, PTH levels were positively associated with all-cause mortality in women with type 2 diabetes (p = 0.006).
The researchers concluded,
“Our new analyses confirmed an independent relationship between low vitamin D levels and all-cause mortality in men with diabetes. This relationship was still statistically significant also when two other well-established risk markers for mortality, PWV and carotid IMT, were added to the analyses.”
They went on to state,
“This suggests that vitamin D can be used as a surrogate marker of risk for mortality in male patients with type 2 diabetes.”
While the study did not find a significant relationship between vitamin D status and mortality in women with type 2 diabetes, it is important to acknowledge the inverse relationship between vitamin D levels and PTH levels. The study may not have held enough power to determine significance between vitamin D levels and mortality, since only nine women died during the six years of follow up.
Strengths in the study include the use of registry data on mortality with no patients lost to follow up. Also, it is the first study of its kind to measure PTH and calcium levels in conjunction with vitamin D. On the other hand, the study had a few limitations to keep in mind. The short follow up meant that there were low rates of mortality. Furthermore, the findings just prove an association; they do not prove that low vitamin D status causes mortality in men with type 2 diabetes.
Jennersjö P., et al. A prospective observational study of all-cause mortality in relation to serum 25-OH vitamin D3 and parathyroid hormone levels in patients with type 2 diabetes. Diabetology & Metabolic Syndrome, 2015