For the past few years, about once a year, I've been getting horizontal ridges in my big toe nails. At first I thought it was just due to extreme cold, because for a couple winters we didn't have heat. But the ridges have come back again. I'm assuming it's a vitamin deficiency, but I'm not sure what. Anytime I've had blood work done I've been told everything looks fine - except once several back when my vitamin D looked low. That was back when I had fewer vitamin D fortified things in my diet. I have a healthy vegan diet, and the supplements I take regularly are: B complex, calcium and magnesium (not the full dose, though), iron, and DHA/EPA. I've just bought some vegan D2 supplements from Vega, thinking maybe the fortified soy milk isn't enough.
Any suggestions for what might be causing the ridges?