I previously posted about how a controlled trial showed that adequate amounts of vitamin D prevents cancer in postmenopausal women - though it hasn't been tested in other population groups, or in the absence of calcium. Now I've found a plausible theory for why sufficient vitamin C should be expected to prevent heart disease - though I can't find any evidence that it's ever been tested in humans at all.
The only reason I even looked at this theory is because of the author: Linus Pauling. While Pauling wasn't right about all his theories, he was correct often enough to pay some attention to them.
Pauling believed that heart disease was connected with vitamin C - or rather, the lack of vitamin C. More specifically, he thought that human predisposition to atherosclerosis was an evolutionary reaction to periodic vitamin C deficiency. To understand the theory, we need to understand a bit more background information on vitamin C.
Vitamin C is needed for synthesis of collagen, which holds certain tissues together. One of these tissues is blood vessel walls; this is why bleeding from mucus membranes is a symptom of severe vitamin C deficiency in the form of scurvy.
Most animals synthesize their own vitamin C from glucose. Primates are an exception; primates have lost the ability to synthesize vitamin C, likely because vitamin C is available in fruit and most primates are frugivores.
Unfortunately, humans are not primarily frugivores, so we don't get as much vitamin C as most primates. Pauling's theory is that atherosclerosis is an adaptation to the lack of sufficient vitamin C in the human diet: when vitamin C is low, fats deposit on artery walls to help compensate for increased permeability from lack of collagen synthesis. Pauling posits that this resulted from more seasonal availability of fruit as humans migrated out of the tropics, but given what we now know, it seems more likely that any such adaptation happened due to dietary shifts, perhaps the shift to meat as a major food source in the early paleolithic.
If true, how much vitamin C do we need? Pauling gives a figure for vitamin C synthesis in those animals that synthesize it of about 5% of glucose intake. A percentage may be appropriate because glucose and vitamin C are very similar chemically, and often compete for the same receptors. Some wild fruit from the tropical Americas have vitamin C at levels as much as 10% of their carbohydrate content. Baobab fruit, available on the African savannahs on which humans likely evolved, are between 1% and 5%. Pauling himself took 3g per day until his death at 93, which was probably between 1% and 5% of his carbohydrate intake. Domesticated fruit are generally below 1% - strawberries and kiwi fruit coming close to 1% - with lemons at 2%. That may be more in line with what we need, if we have adaptations to low dietary vitamin C as Pauling posits.
Of course, while there are plenty of epidemiological indications that more fruit may help reduce heart disease - often attributed to antioxidants, and vitamin C is a strong antioxidant - none of this has been subjected to intervention experiments. Without such experiments, it's difficult to say whether vitamin C will actually help. Still, if you eat a lot of starchy food, vitamin C might be something to consider.
A recent result: