Can you solve this Medical Mystery?

~87 year old man

~Feels dull, aching pain in back and pelvis

~Arms and legs are sore

~Muscles feel weak

~Only goes outdoors on days when there is overcast

~Has celiac disease

~Doesn't drink milk

~Has two broken ribs after tripping and hitting his chest on his walker

~Has loose transformation zones on bones

~Blood and urine tests showed abnormal levels of Vitamin D, Calcium, and Phosphorus