The most common question I get is, "Can you just give me a big dose of a brain supplement without any research and not worry about what the side effects are?"
The short answer to that is yes and no. If you have an imbalance in your system (for example, too much or too little calcium), a small dose of vitamin D and magnesium can help. But if you have more than your body needs, then the dose you give needs to be bigger than the amount your body can handle. This is why we have vitamins B12 and D for healthy bones and teeth, and also for healthy nerves and eyes. If you have too much, you get sick and your brain becomes less efficient.
But most of the time, if you have a high calcium and low magnesium, you are likely fine. The important thing is to take the correct doses.
Vitamin D is the most important vitamin for the brain, and magnesium helps balance calcium. The key word is the dose. It may take weeks of a high dose to bring the desired effect, but a low dose will do. There are more supplements you can buy that will help, but the key thing is to find out what works best for you and what is not helpful. The brain can only survive a little. A little goes a long way.