Oxalates are natural compounds in some plant foods that can bind to calcium in the body. Excess oxalates may form calcium oxalate kidney stones—8 in 10 stones are this type. High-oxalate foods include spinach, beets, rhubarb, and black tea. To reduce risk, stay hydrated, limit salt and protein, avoid high-dose vitamin C, and eat calcium-rich foods like broccoli and kale with meals. Proper cooking can reduce oxalate content in plant foods.

Vitamin D insufficiency has reached epidemic proportions and has been linked to low bone mineral density, increased risk of fracture, and...