The single mother would be considered to be a member of lower class. In addition, a class system employs a social ranking established primarily on economic position and a system of stratification below which country-dwellers were obligatory to work land rented to them by nobles in altercation for military protection was recognized as estate system.
Vitamin D mostly helps the body absorb calcium (which we need for strong bones) and helps keep immune systems strong. Vitamin D deficiency leads to more flu and colds, fragile bones, weak muscles, high blood pressure and depression. Deficiency can lead to hundreds of diseases.
Hope this helps! :)