Why the Body Needs Vitamins

The food we eat provides more than just energy. Alongside the carbohydrates, fats and proteins that fuel and build the body, our diet must supply a range of substances needed in much smaller quantities but no less essential to health. Among the most important of these are vitamins. A vitamin is an organic compound that the body requires in tiny amounts to work properly, and which, in most cases, it cannot make for itself. Because the body cannot manufacture them, or cannot make enough, vitamins must be obtained from what we eat. Although the amounts involved are minute compared with the bulk of our food, a shortage of even one vitamin can lead to serious illness.

Vitamins do not provide energy in the way that sugars or fats do. Instead, they act as helpers in the countless chemical reactions that keep the body running. Many of them assist the enzymes that drive these reactions, allowing processes such as releasing energy from food, building tissues and repairing damage to proceed smoothly. Without the right vitamins, these reactions slow down or fail, and the effects can appear throughout the body, from the skin and eyes to the bones and nerves.

Scientists usually divide vitamins into two broad groups according to what they dissolve in. Fat-soluble vitamins dissolve in fat and can be stored in the body's fatty tissues and in the liver. Because they are stored, a person can draw on these reserves during periods when the diet is poor, and it is not essential to consume them every single day. Water-soluble vitamins, by contrast, dissolve in water and are mostly not stored in any quantity. Any excess is generally removed from the body in the urine, which means these vitamins need to be replaced more regularly through the diet.

This difference between the two groups has practical consequences. Because fat-soluble vitamins are stored rather than excreted, taking very large amounts of them, usually in the form of supplements, can allow them to build up to harmful levels. Water-soluble vitamins are less likely to accumulate in this way, since surplus amounts are usually flushed away. It is a common belief that vitamins can only ever do good and that more is always better, but this is mistaken; with certain vitamins, a large excess can be as damaging as a shortage.

The consequences of vitamin deficiency have been known, in their effects if not their cause, for a very long time. Sailors on long voyages, cut off from fresh food for months, often fell victim to a disease that made their gums bleed and their wounds refuse to heal. It was eventually found that eating certain fresh fruits and vegetables prevented and cured the condition, long before anyone understood that the missing ingredient was a specific vitamin. Other deficiency diseases affect the bones, the skin, the nervous system or the blood, and each is linked to the lack of a particular vitamin.

Different foods are rich in different vitamins, which is one of the strongest arguments for eating a varied diet. Fruits and vegetables, whole grains, dairy products, eggs, fish and meat each contribute their own mixture, and no single food contains everything the body needs. One vitamin is unusual in that the body can produce it with the help of sunlight falling on the skin, so that in this case diet is not the only source. For most vitamins, however, food remains the reliable supply, and a diet drawn from a wide range of foods will normally provide all of them in the amounts required.

The way food is stored and cooked can affect how much of its vitamin content survives to be eaten. Some vitamins, particularly certain water-soluble ones, are fragile and can be reduced by prolonged heating or by being dissolved away in cooking water. Vegetables that are boiled for a long time may lose a portion of their vitamins into the water, which is then poured away. Gentler methods of cooking, and eating some foods raw where that is safe, help to preserve more of what the food originally contained.

For most people eating a reasonable and varied diet, deficiency is uncommon, and there is no need to worry about each individual vitamin. Supplements can be valuable for those with particular needs, but they are not a substitute for good food, which supplies vitamins alongside many other beneficial substances. The best approach for the majority is simple: eat a broad range of fresh, minimally processed foods, and the vitamins will largely take care of themselves.