Brief Answer:
if you have deficiency then it's important to take them

Detailed Answer:
Hello,

let me start with a common misunderstanding. The body does not need more vitamins or iron than the body requirements. If you're deficient in vitamins then you do need supplementation. The same applies for iron. If you have sufficient amounts of vitamins and iron then taking more may even hurt you. So the question is how do you know that you don't have any vitamin or iron deficiency?

Iron deficiency is very easy to diagnose with a simple blood test but it may also be evident by its effects on the body. Anemia is a common finding in patients with iron deficiency which may cause fatigue at first and then more symptoms like tachycardia, headache, difficulty to concentrate, etc.

Vitamin deficiency is not as easy to diagnose because although there are tests for vitamins, the clinical diagnosis is not as straightforward. We can suspect certain deficiencies like B1 or B12 but some of the rest of the B-complex vitamins cannot be assessed easily.

A basic 'rule' to follow is to try to eat a balanced diet that is to eat all kind of nutrients. Eating red meat once a week is more than enough. Poultry (and other 'white' meat) can be eaten 3-4 times per week. Legumes and the like may fill the rest of the days. A salad should always be on your table. Dairy products and fruits should be consumed every day.

So if you follow the aforementioned instructions you're not supposed to be deficient in iron or vitamins. If your doctor suspects deficiency then testing may prove it and then you'll have to find out why it occurred. For example the much more common iron deficiency can be caused by latent blood loss from the gastrointestinal tract (ulcers, angiodysplasias, polyps, cancer, etc).

Certain drugs may increase suspicion for deficiencies. For example metformin (for diabetes) may reduce vitamin B12 amounts in the body by preventing its absorption. Heavy alcohol consumption may impair more than 1 vitamins including vitamins B12 and B1. etc...

Taking more iron than the required amount (enough to replenish the iron stores (which is approximately 1mg per day) may end up in iron accumulation in various organs and iron toxicity. Vitamins of the B complex are not as dangerous as iron so even if you take more than the required amounts the risk of harm would be low.

I hope you find my comments helpful!
Kind Regards!

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