For me even as much as 5g ascorbic acid daily causes awful massive diarrhoea, even 2.5g daily is too much, while most people here seem to report needing many times this amount. As the amount of vitamin C we need is based on oxidative stress, I'm thinking that diet has a big role in your requirement for vitamin C?
My diet is very different from a 'normal' one, it is high-fat moderate-protein very-low-carb and carnivorous. I eat meat, fat, eggs, dairy, home-made broth, the only non-animal foods I eat are coconut oil, salt, and herbs/spices. I average 80-100g protein, 3-5g carbs, 180-200g fat, or about 20%, <1%, and 80% of calories respectively.
As oxidation is a major factor in vitamin C requirement, then hyperglycaemia would increase in need for vitamin C a lot. When carbohydrates are eaten, even a 'whole grain' starch, it is digested into glucose very quickly (peak blood glucose being ~30-35 minutes after ingestion), and once blood sugar raises above 130mg/dL or 7.2mmol/L then glycation greatly increases. This is why HbA1c is a good estimate of average blood glucose, it is a measure of how much of your haemoglobin is glycated, and as the overturn of haemoglobin is about 3 months to gives a good estimate of average blood glucose over that period. So HbA1c could be used as a measurement of oxidation in the body, along with over tests such as CRP, liver enzymes, etc. My HbA1c was last tested as 25mmol/mol or 4.4%, this corresponds to an AVERAGE blood glucose level of 4.4mmol/L or 79.2mg/dL.
It's very interesting that people eating no carbohydrates, aka a purely carnivorous diet don't get scurvy, even after decades. One such example is the Inuit people who eat nothing but meat, seal, and fish. An explorer called Stefansson lived with the Inuit for many years, noting that they did not suffer from obesity, diabetes, or heart disease, and even underwent a study at the Bellevue Hospital to demonstrate the lack of scurvy and other deficiencies of eating a carnivorous diet. You can read the study here: LINK
It's also interesting that heart disease is only a NEW disease, yet we;ve lacked the ability to make ascorbic acid for thousands and thousands of years. When Augustus Waller invented the ECG in 1911 to detect heart attacks, he was told that there was no market for such a device and to stop wasting his time. Similarly animals that do produce ascorbic acid can develop heart disease if fed an inappropriate diet, such as cats and dogs, which are carnivores, being feed a diet of processed grains (dry pet food); on such a diet they get all the same diseases that have become 'epidemics' to us in the last half century such as obesity, diabetes, and heart disease. The research that concluded fat and cholesterol are the cause of heart disease was done on rabbits, feeding any animal the wrong diet will produce these disease; carnivores don't get fat and sick from a diet of meat, but do from high carbohydrate foods like grains and other starches.
But even herbivores get sick from high carbohydrate diets. Cattle are fed grains, corn, and soy in CAFOs to fatten them up as quickly as possible, but their immune system decreases and antibiotics have to be added to the fed, they must also be killed at the right time as too late means they will die of liver failure and thus their meat isn't allowed to be sold. Cattle's natural diet is grass, which is high in fibre and protein, and low in fat and non-fibre carbohydrates. But a herbivore's diet is different from what it eats, as ruminants have rumens and other herbivores large colons which ferment fibre into short-chain fatty-acids such as butyric acid (named after its presence in butter). Non-ruminants get ~65% of their calories from these short-chain fatty-acids, and ruminants even more as the fermenting happens early in the digestive process! A gorilla for example with receive a diet of ~66% calories from fat, 21% from protein, and 13% from carbohydrates. This means that ALL mammals eat a high fat diet, carnivores directly and herbivores via fermentation. More info: http://www.second-opinions.co.uk/should ... -diet.html
As we lack both a rumen and a large colon, and that the largest part of our digestive system is the small intestine with a very small colon (see: http://roarofwolverine.com/wp-content/u ... ateGut.jpg
), this shows that humans are clearly not designed to ferment fibre, and thus must get our fat directly through diet.
Until very recently humans ate a lot of animal fats, 100 years ago vegetable oils (a misnomer, all vegetable oils are in fact grain/seed oils, there is no broccoli oil (fyi: corn is a grain!)) hadn't been invented. Just read any really old cookbooks, they all call for large amounts of lard, tallow, butter, cream, etc. Yet no-one was getting obese, diabetic, or heart disease. Graph: http://www.lewrockwell.com/miller/us-dietary-fat.gif
After Ancel Keys did his 7 countries study showing a positive correlation between fat intake and heart disease (even though correlation does NOT imply causation, and the fact that he has data from over twenty countries which showed there was NO relationship between the two), and the McGovern report concluded that all Americans should eat a low-fat diet to prevent heart disease (even though there was no real data that fat caused heart disease but they didn't have the time to wait until proper data was collected). So for the last half century we've been told to eat less fat, and more grains, and what's happened? Obesity, diabetes, and heart disease have sky-rocketed. We're even now seeing adult-onset diabetes in young children, so they had to change the name to type 2 diabetes!
So if lack of vitamin C is the cause of heart disease, why does it occur in animals such as cats and dogs which CAN make vitamin C when they're fed a high-grain diet; why was heart disease non-existent until recently when the population adopted a low-fat high-grain diet; and why were the Inuit free of heart disease and scurvy eating nothing but meat?
I've done a lot of nutritional research over the years, which amongst other reasons is why I eat the way a do, and recently been working on why people eating all meat diets don't get scurvy. Sailors who got scurvy, which could kill them in about two months, were eating diets of dried (not fresh) meat, biscuits, and rum. I've written a summary of why an all meat does not produce scurvy while a sailor's diet does on my blog: http://mostlymeatiswhatieat.blogspot.co ... otein.html
My post talks a lot about glutathione which is the most powerful antioxidant in our body, much more than ascorbic acid. As glutathione is greatly increased on a diet high in meat, this means there is less need for ascorbic acid as an antioxidant. Although not said in my post, I have recently found out that glutathione also regenerates ascorbic acid which would decrease your required intake.
Additionally the pathway by which ascorbic acid enters cells (GLUT1) is also used by glucose, such that hyperglycaemia would result in the glucose out-competing the ascorbic acid and thus increases the need for ingested ascorbic acid.
Heart disease is not the result of cholesterol simply goo-ing up blood vessels, if it were then plaques would occur randomly over the body, but are instead mostly around the heart (if it were random then by pass surgery wouldn't work (using a leg vein to reroute around a blocked coronary artery)). Atherosclerosis actually starts when the artery is damaged, such as by hyperglycaemia, then the cholesterol plaque acts like a plaster to heal the wound heal, and indeed ascorbic acid helps in the healing of the artery. Heart attacks happen when the cholesterol plaque comes loose and then blocks the blood vessel. But blaming heart disease on cholesterol is like blaming a cut on a plaster or a fire on the firemen.
You wouldn't need so much cholesterol or ascorbic acid to repair the damage if less damage is being done in the first place. And indeed low-carbohydrate diets produce a greater drop in total cholesterol (while increasing HDL 'good' cholesterol) in clinical trials, while the low-fat diets show a decrease in HDL cholesterol.. So by removing/reducing carbohydrates, less cholesterol is needed, and as most of the cholesterol in our blood is made my the liver not from our diet (200mg/dl is considered the border for high cholesterol, and this translates to ~10 grams of cholesterol in the whole blood, which is huge compared with the 300mg limit on cholesterol intake the USDA advises), then it's clear why cholesterol levels drop when less damage is being done due to less hyperglycaemia from a lower carbohydrate intake.
HbA1c levels are HIGHLY correlated to heart disease risk, and while I did already say that correlation does not imply causation, from low-carbohydrate clinical trails we are starting to get evidence that lowering HbA1c via restricting carbohydrates actually reduces heart disease risk a Lot more than a low-fat high-grain diet does.
Of course there are other things that cause damage to the arteries other than hyperglycaemia, such as omega-6 fatty-acids, see: http://perfecthealthdiet.com/wp/wp-cont ... -6-CVD.gif
This is why vegetable oils are so unhealthy, as they contain HUGE amounts of omega-6 fatty-acids, while animal fats (and tropical oils such as coconut and palm oils) are very low in omega-6 fatty-acids: http://3.bp.blogspot.com/_tMgToYs_oYc/T ... ontent.PNG
and http://ckresser.wpengine.netdna-cdn.com ... ntoils.png
The level of linoleic acid (an omega-6 fatty-acid) in human body fat has been increases over the years due to vegetable oil consumption: http://3.bp.blogspot.com/-W1ytkwstPQo/T ... dy+fat.jpg
Saturated fats can't be oxidised, as oxidations can only effect fatty acids with double bonds, during oxidation the double bond is broken and new stuff added to the now free bonds. This is why animal fats and tropical oils are the safest fats to eat as they are high in saturated fats, and low in omega-6 fatty-acids. This makes them the most heat stable and best with which to use in cooking.
So a diet high in glutathione precursors, low in carbohydrates, high in saturated fat while low in omega-6 fatty-acids would mean that very little or even no ascorbic acid is needed in one's diet, as evident by the lack of scurvy and heart disease in populations eating a carnivorous diet and modern people eating a 'zero carb' carnivorous diet.