If you’re low on B-12, vitamin D, and Omega-Fats, this can cause cognitive issues. These deficiencies contribute to brain fog, anxiety, depression, and memory loss. Omega-3 is important as it helps the heart and the brain to function. It can also reduce the risks of Alzheimer's. Sardines, salmon, tuna eggs, and cocoa good are brain foods. Low vitamin can also impair memory. WebMD offered some guidance for your “Ds” “…daily intake of vitamin D for older adults is 600 to 800 IU, according to the U.S. National Institutes of Health. Vitamin D, called the sunshine vitamin, is found in fortified foods, such as milk, orange juice, cereals and yogurt.