Vitamin C is a water-soluble vitamin which cannot be stored in the body, so a regular intake is essential. Dietary sources include most fruit and vegetables including citrus, berries, blackcurrants, capsicum peppers, kiwi fruit and green leafy vegetables.
Vitamin C acts as an important antioxidant in all body tissues, and is needed for at least 300 metabolic reactions to work properly, including the production of collagen to maintain elastic arteries. It is also involved in the metabolism of stress hormones. New findings also suggest that vitamin C is involved in regulating levels of fibrinogen – a circulating protein that increases the likelihood of blood clots.
Studies show that men and women with the highest dietary intakes of vitamin C have a lower risk of developing high blood pressure, coronary heart disease and stroke.
Why don’t we make our own?
Most animals make their own vitamin C, but humans and other primates lack the enzyme (L-gulonolactone oxidase) needed for its synthesis. The goat, for example, which weighs around the same as a man, normally produces between 2 and 13 g of vitamin C per day and synthesis dramatically increases during times of physical stress and illness. Quite why humans have either lost, or never acquired the ability to synthesize our vitamin C requirements remains one of the greatest mysteries of human biochemistry. It is thought to have resulted from a genetic accident millions of years ago. This genetic defect also increases the risk of a number of other common illnesses such as viral infections, raised cholesterol levels, coronary heart disease and cancer as well as reducing our ability to cope with stress.
Because our primitive ancestors ate a vegetarian diet full of vitamin C-rich plants such as purslane (just 100 g of which contained 27 mg vitamin C), their vitamin C intake was much higher than is found in the modern diet, and estimated at 392 mg a day. This high dietary intake meant they were able to obtain adequate amounts from their diet.
Vitamin C protects against heart disease
Lack of vitamin C is a risk factor for heart attack and stroke. Data from 15 trials suggest that people with the highest intake of vitamin C, from both diet and supplements, have a 16% lower risk of coronary heart disease than those with the lowest intakes.
A recent study in Norfolk, UK, involving over 19,000 adults aged 45 to 79 years found that circulating levels of vitamin C were inversely related to death from all causes over the 4 year study period. The researchers concluded that even relatively small increases in vitamin C concentrations may have a measurable effect on risk of a fatal heart attack; for example, eating an orange a day was estimated to reduce the risk of coronary heart disease by as much as 10%.
The EU RDA for vitamin C is 80 mg. An expert scientific panel in the US have suggested that the intake needed to meet the requirement of half the healthy individuals in a population is 100 mg/day, with a safety margin giving a proposed daily amount of 120 mg/day. The recommendation is 100mg per day in Austria, Germany and Switzerland. The upper safe level for long-term use from supplements is suggested as 1000mg. Higher doses can cause indigestion and have a laxative effect. These are largely due to the acidity of vitamin C itself and are not a sign of toxicity.
The absorption and metabolism of vitamin C varies depending on the amount consumed. At intakes of up to 200 mg/day as a single dose, absorption of vitamin C is almost complete through an active transport process. At single doses of over 500 mg, it is also absorbed through a process of diffusion, but efficiency of absorption declines as the dose increases. As a result, only half of a 1.5g dose is absorbed (ie 750mg).
To achieve optimum vitamin C absorption and retention, higher doses (above 1000mg per day) are best taken spread over several doses per day.
Healthspan’s Vitamin C with Bioflavonoids are delicious, chewable tablets with an orange/apricot flavour. Made to pharmaceutical standards, they are sugar and aspartame-free (sweetened with sucralose). Each tablet supplies 500mg vitamin C plus bioflavonoids to boost absorption and effectiveness.
Check price for 320 tablets at Healthspan.co.uk
A similar product in the US is Natures Aid Vitamin C with rosehips and citrus bioflavonoids. Check price for 50 sugar free, chewable 500mg tablets at Amazon.com
Solgar’s Ester-C Plus tablets contain a non-acidic, highly absorbable form of vitamin C that helps to prevent digestive irritation for those who experience indigestion with the normal, ascorbic acid form. Each tablet provides 1000mg vitamin C plus bioflavonoids.
● If you are taking vitamin C and need to have a urine test inform your doctor that you are taking supplements as it can affect laboratory results.
● Some urine test kits used by diabetics are also affected by high dose vitamin C – use a kit that is not affected.
● High-dose vitamin C may mask the presence of blood in stool tests – inform your doctor if you are advised to have one of these.
● People with iron-storage disease (haemochromatosis) should only take vitamin C supplements under medical advice.
● Recurrent stone formers and sufferers of renal failure who have a defect in ascorbic acid or oxalate metabolism, should restrict daily vitamin C intakes to approximately 100 mg.
● Anyone who is taking a very high-dose supplement and needs to reduce their vitamin C intake should do this slowly over a few weeks rather than stopping suddenly, in order to avoid a so-called ‘rebound scurvy’ effect. A sudden reduction in blood vitamin C concentration means that enzymes activated by high levels of vitamin C are suddenly deprived of the extra vitamin C they need to work properly, and this can produce temporary symptoms of vitamin C deficiency.
If your blood pressure is borderline or raised, self-monitoring is key to maintaining good control.
Click here for advice on choosing a blood pressure monitor to use at home.
Image credit: miwa-in-oz; lerch&johnson / shutterstock