Vitamin D is a superstar for bone health, immune support, and mood regulation. But unlike water-soluble vitamins, D is fat-soluble. That means it can accumulate in your body, and an overdose isn’t flushed out—it sticks around. Chronic high doses (over 10,000 IU daily) can raise calcium levels in blood, leading to hypercalcemia. Signs include nausea, vomiting, and in severe cases, cardiac arrhythmias.

Over time, hypercalcemia can calcify your arteries—turning them into rigid tubes that make your heart work harder to pump blood. That’s a direct path to hypertension and potentially atherosclerosis. So yes, something as innocuous as vitamin D can mess with your heart if you’re not paying attention.

Dosage note: Most adults need 1,000–2,000 IU per day. If you’re taking more, get your blood levels checked every few months.