When sunlight is scarce
During the summer, the body can convert sunlight from just ten to 15 minutes of daily exposure into ample amounts of vitamin D. From the beginning of October through March, however, that’s not possible in much of North America, when the angle of the sun sinks lower into the southern hemisphere and daylight becomes more scarce. So you may need to up your consumption of vitamin D-rich foods in the winter (even if you’re spending lots of time outside building snowmen!). The current recommendation is 400-600 IU (international units) per day. Plus, learn some more ways to eat more vitamin D-rich foods.
A hundred grams of mushrooms provide some vitamin D, so freely toss them in your food. But for the biggest boost, some growers produce special Portobello mushrooms that have been exposed to a flash of UV light to increase the content of the vitamin. You can even sprinkle on the benefits with Portobello mushroom powder.