Dude, you should not be taking vitamins or any other medication while fasting.
If you have not done even this much research, and have plunged headfirst into a 40-day water fast, you are taking a big risk.
I strongly recommend that you end your fast at 8 days. Then refeed and try to stay on a good diet. Then see about another fast after that.
Your comments indicate someone who does not know enough, and no one's first Water Fast should be 40 days unless they are Stage 4 cancer and have just 6 months to live.