There are many important vitamins but I see using Vitamin D and K2-MK7 to get our Vitamin D levels up into the 70-100 range as the first step to better health and weight loss. It was once thought levels greater than 30 were OK but now 50 is considered at the minimum level of Vitamin D levels to prevent premature death from disease.
http://www.medicalnewstoday.com/articles/161618.php
Vitamin D3 is dirt cheap in the USA. I was stuck in the 20's level for much of my life I guess until 2014 when I finally realized being critical low in Vitamin D levels was associated with most all forms of premature death.
http://drgominak.com/vitamin-d-hormone/
This website has a lot of good Vit D3 details worth reading.