Already known as a powerful superfood, kale helps to strengthen bones during times when our body does not get enough sunlight for vitamin D conversion. (mindbodygreen.com)
Most people in the upper half of the northern hemisphere don't get enough sunlight during winter and most of spring and fall as well. (health.harvard.edu)
It's not easy getting enough sunlight when you're indoors all day working or going to school. (susancnt.com)