Nearly 115 million Americans are currently on the road to type 2 diabetes. Not there yet — but heading in that direction, often without symptoms, often without awareness, and often without meaningful intervention beyond being told to eat better and lose some weight.
According to the International Diabetes Federation, approximately 537 million adults worldwide were living with diabetes in 2021. That number is projected to rise to 783 million by 2045. The Caribbean is experiencing one of the most serious diabetes epidemics in the world relative to population size. In several Caribbean nations, diabetes prevalence among adults exceeds 15 percent — significantly above the global average of approximately 10 percent. The Cayman Islands is not immune.
What the Study Found
Published in JAMA Network Open, this research builds on the Vitamin D and Type 2 Diabetes Study — a randomised controlled trial that followed more than 2,000 American adults living with prediabetes. Participants received either 4,000 IU of vitamin D daily or a placebo for up to three and a half years.
Initially, looking at the group as a whole, the results were underwhelming. No significant difference across all participants. But when researchers analysed participants’ DNA, a considerably more interesting picture emerged.
There is a variation in a gene called ApaI that influences how effectively the body responds to vitamin D. Approximately 70 percent of the prediabetic adults carried specific variations — known as AC or CC — that made them genuinely responsive to supplementation. In this group, high-dose vitamin D produced a 19 percent lower chance of developing type 2 diabetes over the course of the study. The remaining 30 percent — those carrying the AA variation — saw no benefit at all. The same supplement, the same dose, the same duration. Zero measurable effect.
This is what personalised medicine looks like in practice. Not one recommendation for all, but understanding which tool works for which body — and why.
Why Vitamin D and Blood Sugar Are Connected
Vitamin D receptors are present in an extraordinary number of cell types — including, critically, the beta cells of the pancreas. These are the cells responsible for producing and releasing insulin. When vitamin D binds to its receptors in pancreatic tissue, it facilitates the insulin release that regulates blood glucose. Put plainly: vitamin D helps the pancreas do its job. In a state of deficiency, that function is impaired. Blood glucose regulation becomes less efficient. Insulin resistance deepens. The metabolic trajectory toward diabetes accelerates.
The COVID Connection
Across multiple studies conducted during the pandemic, vitamin D deficiency emerged as one of the most consistent factors associated with severe COVID-19 outcomes, hospitalisation, and death. The mechanism is immunological: vitamin D regulates the inflammatory response, supports the innate immune system’s first-line defence against viral infection, and helps prevent the excessive inflammatory reaction known as the cytokine storm that was responsible for many of the most devastating COVID outcomes. This deserved, and still deserves, a more prominent place in the clinical conversation than it received.
A Brief Word on Statins
A significant proportion of those who experienced the worst COVID outcomes were on statin medications. What is less commonly discussed is that the cholesterol synthesis pathway statins inhibit is the same pathway involved in the synthesis of vitamin D. Cholesterol is the precursor molecule from which the body manufactures vitamin D in response to sunlight. Some research suggests that long-term statin use may therefore contribute to or compound vitamin D deficiency. Statins have genuine, evidence-based benefits for specific populations — but the intersection of statin use, vitamin D status, immune function, and metabolic health is a conversation worth having with your prescribing physician.
What This Means for You Practically
Get your vitamin D level tested. Ask for your 25-hydroxy vitamin D level at your next blood draw. This is the non-negotiable starting point. If you have prediabetes, ask about the ApaI genetic variant. A simple genetic test may tell you whether you are in the 70% who will benefit from high-dose supplementation or the 30% for whom it will not move the needle. Do not supplement blindly at high doses. 4,000 IU daily should not be undertaken without knowing your baseline levels and ideally with clinical oversight. Prioritise dietary sources and sensible sun exposure. Fatty fish, egg yolks, beef liver, and UV-exposed mushrooms are valuable dietary contributors.
“The art of medicine consists of amusing the patient while nature cures the disease.” — Voltaire (though in this case, the science is catching up to nature in ways worth paying careful attention to.)
References: Dawson-Hughes et al. (2025) JAMA Network Open · Pittas et al. D2d Study, Tufts University · Merzon et al. (2020) FEBS Journal · Hernandez et al. (2021) Journal of Clinical Endocrinology & Metabolism · Holick (2007) NEJM · Fung (2016) The Obesity Code.
This blog is for informational and educational purposes only and does not constitute medical advice.