Tight diabetes control doesn't prevent heart disease in long-term type 1 patients

A group of people who have lived with type 1 diabetes for more than half a century without developing kidney damage ought to be a success story. They have kept their blood sugar, blood pressure, and cholesterol in excellent control—the three pillars of cardiovascular protection. Yet when researchers at Joslin Diabetes Center and Harvard Medical School examined over a thousand of these long-term survivors, they found something that upended the conventional wisdom: roughly four in ten of them have heart disease anyway.

The finding, presented at ENDO 2024, the Endocrine Society's annual meeting in Boston in June, challenges the assumption that tight metabolic control is sufficient to prevent heart damage in people who have managed type 1 diabetes for decades. Marc Gregory Yu, the study's lead researcher, and his colleagues were studying a cohort known as the "Medalists"—individuals from across the United States who have lived with type 1 diabetes for over fifty years. What made this group remarkable was not just their longevity, but their restraint: only thirteen percent of them had developed kidney complications, and most maintained the kind of blood sugar, blood pressure, and cholesterol numbers that doctors consider ideal. Yet despite this, approximately forty percent reported having heart disease.

To understand what was happening beneath the surface, the researchers used imaging to look directly at the heart. A subset of 153 Medalists underwent CT scans to measure calcium deposits in the coronary arteries—a marker of atherosclerosis and cardiovascular damage. Another 111 underwent MRI imaging to assess the heart's structure and its ability to pump blood. The CT findings were striking: the Medalists showed higher levels of calcium buildup in their coronary arteries compared to other people of similar age who also had type 1 or type 2 diabetes. Yet their hearts' actual structure and function looked comparable to their peers. This suggested that damage was accumulating in the blood vessels even as the heart itself continued to work normally.

The research also revealed that among the Medalists, higher blood sugar levels—even within what is considered good control—were closely associated with the presence of heart disease. This observation underscores that blood sugar management remains critical even as people age with diabetes, though it also hints that the relationship between glucose and heart damage may be more complex than previously understood. Yu noted that the risk factors for heart disease appeared to differ depending on whether a Medalist had developed kidney complications, and that these patterns differed again from what is typically seen in people with type 2 diabetes.

The implications are sobering and practical at once. As medical care has improved, more people with type 1 diabetes are living into their sixties, seventies, and beyond. A substantial proportion of them will never develop kidney disease—traditionally the most feared complication. But the Joslin study suggests that this reprieve from kidney damage does not guarantee protection from the cardiovascular system. The heart remains vulnerable even when the kidneys are spared and even when the numbers on a blood test look good.

Yu and his team suggest that these findings may point the way toward new medications designed specifically to protect the hearts of people with type 1 diabetes, rather than relying on drugs developed for other populations or other forms of diabetes. The conventional risk factors—blood sugar, blood pressure, cholesterol—are necessary but apparently not sufficient. Something else is driving heart disease in this population, something that remains to be identified and addressed. Until that happens, long-term type 1 diabetes survivors face a puzzle: they have done everything right, and their hearts are still at risk.