Slightly more complex set of B vitamins many types.(water soluble)
now every B of the complex has its own benefits
B12 is great for nerves and is great if you looking to shed some pounds/kilos: gives you energy to increase your exercising capabilities,
If you had a gastric bypass you have no stomach acid so you have to supplement it all your life.
make sure you understand that if you are on Metformin or antacids they may decrease absorption.
If you are vegetarian you need it period.
B6 is great for kidney functions , nerves, alcoholics, PMS: found in meat, poultry,fish and fruits, cheese: 1.3-1.5 mg per day usuallu a good multivitamin will have it.
B3 is excellent for reducing choelsterol especially if you have elevated triglycerides.
B1 is very essential for people who like alcohol or have a poor appetite,diarrhea or have inflammatory bowel disease, canker sores(mouth ulcers). Deficiency can cause serious problems a nervous problem called Wernike Korsakoff syndrome.A good multivitamin will have it along with healthy diet.
Some studies show maybe helpful if diabetics kidneys.
Great vitamin for migranies,burning feet, acne, will increase iron absorption in the body. CAn be found in meats, vegetables,nuts,eggs.
B5:Pantothenic acids:same sources as riboflavin,
Has been used for good skin,ADHD, baldness, asthma ,arthritis,muscle dystropies. Not many studies to warrant above benefits but usually will be present in all multivitamins.
B7:Also called BIOTIN great for hair and nails. and hormone synthesis.
B9:folate: I think everyone knows about this one, very essential for all women of child bearing age to prevent developmental anomalies in the babies in womb. Basically it maintains DNA and Red blood cells.
Alcoholics or people with poor appetite or pregnant or wish to become pregnant need extra 1 mg per day.