Pay attention to the color of your tongue. If it becomes a bright, beefy red (the change can be subtle, but it will be noticeable), you may be low on vitamin B12. This vitamin is essential for making the red blood cells that carry oxygen throughout your body and plays a vital role in maintaining brain function. While researchers aren't sure why a B12 deficiency affects the tongue, you may develop neurological problems, including dementia, if your levels stay low for too long.
Protect Yourself: Meat and dairy products are rich in B12, so if you're a vegetarian or vegan, you may have a harder time reaching your daily allowance. Make sure to take a multivitamin, and consider eating fortified cereals for breakfast (some offer 100 percent of your recommended daily value of B12 in one serving).