Vitamins are classified into two groups: water-soluble and fat-soluble vitamins. Fat-soluble vitamins A, D, E, and K are stored in our liver and fatty tissues. This means we don't have to consume them every day, but there is a risk of them accumulating in the body, which can be harmful.

We cannot store water-soluble Vitamin C and the eight B vitamins: thiamine, riboflavin, niacin, pantothenic acid, biotin, folic acid, and B12, so we excrete the excess through our urine.

Every vitamin is essential, but we must consume water-soluble vitamins every day because we excrete the excess. Fortunately, they are found in many different foods. Besides oranges, Vitamin C is found in broccoli, strawberries, red and green peppers, Brussels sprouts, and even potatoes! We can get B vitamins from whole grains, fortified cereals, rice, oats, liver, meat, fish, dairy products, eggs, potatoes, broccoli, spinach, soy, and legumes. Many of us are low on Vitamin D, which is important for bones, muscles, and immunity. Those at risk of low Vitamin D levels include people who spend little time outdoors, those with dark skin, or those who cover their skin. Food sources of Vitamin D include oily fish, eggs, fortified cereals, meat, and fatty spreads.

Deficiency states can develop. Vegans and some vegetarians, for example, are at risk of Vitamin B12 deficiency, as this vitamin is found mainly in animal products. B12 deficiency can lead to fatigue, depression, and serious neurological problems. People with diseases affecting nutrient absorption, such as celiac disease or Crohn's disease, can be at risk for many deficiencies, as can those taking certain medications and the elderly; older people are unable to properly absorb nutrients due to decreased stomach acid levels. Smokers may have low Vitamin C levels, heavy alcohol consumers may be low in B vitamins, and overweight or obese people have been shown to have low levels of C, D, B12, and folic acid.

Low levels of key vitamins can lead to vague symptoms such as fatigue, aches and pains, weak immunity, low mood, and skin, hair, and nail problems.

Too much Vitamin A from food or supplements can lead to liver and bone damage and cause birth defects. However, for Vitamin A levels to be harmful, you would need to consume an excess every day for several years. And although we excrete excess amounts of water-soluble vitamins through urine, high Vitamin C levels can cause diarrhea, while too much niacin over a long period can lead to liver damage.

If you take multiple food supplements, be sure not to double up on vitamins - for example, do not take a multivitamin and cod liver oil rich in Vitamin A as well.