The brain requires daily nutrition for optimal performance. If this is not received, mental clarity is affected. Signs of reduced mental clarity include poor memory, trouble recounting specific times or locations, and an inability to cope with stress. Vitamin supplements, a balanced diet, adequate sleep and exercise are ways to achieve mental clarity. Before taking any vitamin supplement, consult with your health care provider to ensure its safety.

Vitamin C

The Alzheimer's Foundation of America advises eating a balanced diet and taking a multivitamin with vitamin C. Vitamin C is shown to support brain health. The human body is unable to make vitamin C and secretes it through urine rather than storing it, so it must be obtained through diet and vitamins every day. In addition, this vitamin is excreted in the urine and not stored. The recommended daily allowance of vitamin C is 90 milligrams. If this is not achieved, a deficiency could result, leading to poor mental clarity.

Vitamin E

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Deficiency in vitamin E impairs the cognitive function of the brain, according to Oregon State University, affecting thought processes and clear thinking. The recommended daily allowance of vitamin E is 15 micrograms. Vitamin E is a fat-soluble vitamin, meaning it is stored in the liver until needed by the body. This vitamin also serves as an antioxidant which protects cells from free radical damage, keeping brain cells healthy.

Vitamin B12

Vitamin B12 levels in the human body are essential to maintain mental clarity and brain health. When vitamin B12 deficiencies occur, disorientation and confusion may result. Vitamin B12 maintains healthy nerves and red blood cells. Nerves are needed in the brain for quick thought responses and red blood cells carry oxygen to the brain. The recommended daily allowance for adults is 2.4 micrograms. This vitamin can be obtained through supplements and diet.