Suggest Ways To Strengthen Weak Knees Due To Deficiency Of Vitamins

I m 43 yrs old. my knees has become week. i can't stand more than 10 minutes. i hav also checked up with doctors in jaipur nd they said u don't hav any problem in ur knees physically. it is deficiency of vitamins but medicines they hav prescribed medicines but no improvement at all last from 6 months.