Dan says one of the secrets of Nicoyans' lifespan can be found in the water that flows through the hills. Their water is among the hardest in Costa Rica—which means it's chock-full of minerals. "Hard water means stronger bones. It also means your muscles are probably working better, especially when you get old," Dan says.
Dr. Oz says hard water has proven benefits. "Calcium, magnesium and water—it relaxes your arteries, it builds bone strength and it has a huge benefit across the board in how your body functions," he says.
Having strong bones is actually one of the most important ways to live a long life. "One of the biggest killers of older people in this country is simply falling down and breaking a bone," Dan says. "If you take calcium and couple it with vitamin D, your bones don't deteriorate as quickly."
To re-create the benefits of the Nicoyans' calcium-rich water, Dan suggests eating eggs and dairy. You can get calcium from other sources too, including leafy green vegetables like kale and broccoli.