Nutrition 101– Vitamins
Nutritionists tend to throw terms like ‘carbs’, ‘vitamins’
and ‘minerals’ around like everyone knows what they are. But
many people, if asked, couldn’t actually tell you what a vitamin
is, or why your body needs them. Yes, organic food usually contains more
vitamins and minerals, but what does this actually mean for your health?
Well, welcome to this series of explanations of the most used nutritional
terms – what they are, what they do, and how to get them. This month:
Vitamins
Vitamins are a diverse group of organic compounds that are involved
in almost every metabolic process in the human body. There are thirteen
known essential vitamins for humans, divided into two groups, the four
fat-soluble vitamins (A, D, E and K) and the nine water-soluble vitamins
(eight B vitamins and vitamin C). In general, fat-soluble vitamins can
be stored in the body, while water-soluble vitamins are not, doing their
job on the way through and then leaving via the urine.
Vitamins act as enzyme co-factors. Enzymes help all the chemical reactions
and metabolic processes in the body actually happen, and without the appropriate
vitamin co-factors, the enzymes, and thus the metabolic processes, don’t
work. You can see how important they are. While we only need tiny amounts
of them, vitamin deficiencies will inevitably lead to metabolic and physical
disorders, including scurvy, anemia, rickets, and birth defects. A good
example of what vitamins can do for you is energy production in your body.
Vitamins don’t provide energy (calories) directly, but they do help
regulate energy-producing processes.
In general, vitamins cannot be synthesized by the human body and must
be obtained from the diet. Examples of vitamins that the human body can
make itself include vitamin A, which can be produced from beta carotene;
vitamin B3 from the amino acid tryptophan; and vitamin D through exposure
of skin to ultraviolet light.
The value of eating certain foods to maintain health was recognized long
before vitamins were identified. The ancient Egyptians knew that feeding
a patient liver would help cure night blindness, now known to be caused
by a vitamin A deficiency. In 1747, the Scottish surgeon James Lind discovered
that citrus foods helped prevent scurvy, a particularly deadly disease
in which collagen is not properly formed, and characterized by poor wound
healing, bleeding of the gums, and severe pain. Yet up until the 19th
century it was widely believed that scurvy was prevented by good hygiene
on board ship, regular exercise, and maintaining the morale of the crew,
rather than by a diet of fresh food, so that Navy expeditions continued
to be plagued by scurvy.
While the human body can’t synthesize most vitamins, plants can,
so fruits and vegetables are excellent sources of many vitamins, especially
vitamin C and the vitamin A precursor, betacarotene. Meat is an excellent
source of A and B vitamins. Dairy is a good source of vitamin D. Good
sources of vitamin E include wheatgerm and unrefined oils.
Overcooking vegetables, especially by boiling, can dramatically deplete
the vitamin C content. Conversely, betacarotene, the pre-cursor to vitamin
A, is often made more bioavailable though cooking (for example in carrots
and red peppers). So the standard nutritional advice is to eat a balance
of raw and lightly cooked vegetables and occasional organic meat and dairy.
Studies have shown that organic produce often contains more vitamin C
than non-organic produce. Other key factors known to influence the vitamin
content of crops include ripeness when picked and time in transportation
or storage since harvest. For example, studies have shown that apples
and apricots picked green contain little or no vitamin C, however if picked
either half or fully ripe the vitamin C content increases to approximately
18 and 60mg per 100g fresh weight respectively. Many vitamins, especially
vitamin C and folic acid, are sensitive to oxidation, heat and light,
and can be rapidly degraded during transportation and storage. For example,
potatoes can lose up to 70 per cent of their vitamin C content in storage.
The take-home message is that fresh is best, so to maximize the vitamins
in your diet, choose fresh, local, organic produce grown in season, and
don’t overcook your food.
Wishing you the best of health,
Shane Heaton
Nutritionist
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