Trillian, places like the World Health Organization and the FDA and other countries' equivalents keep statistics like this. Below is a passage from a 2004 report on
Vitamin and Mineral Requirements in Human Nutrition. The sources are cited so they should be trackable. (When reading try to remember the motives of the WHO is more focused on survival and accute disease prevention than optimal health. So, when they say that 70 mg/day is adequate, well it is adequate for preventing clinical scurvy in most people. However, it' s definitely not optimal.)
<pre>
In Europe and the United States an adequate intake of vitamin C is
indicated by the results of various national surveys (36–38 ). In Germany and
the United Kingdom, the mean dietary intakes of vitamin C in adult men and
women were 75 and 72mg/day (36), and 87 and 76mg/day (37), respectively.
In addition, a recent survey of elderly men and women in the United
Kingdom reported vitamin C intakes of 72 (SD, 61) and 68 (SD, 60)mg/day,
respectively (39). In the United States, in the third National Health and Nutrition
Examination Survey (38 ), the median consumption of vitamin C from
foods during the years 1988–91 was 73 and 84mg/day in men and women,
respectively. In all of these studies there was a wide variation in vitamin C
intake. In the United States 25–30% of the population consumed less than 2.5
servings of fruit and vegetables daily. Likewise, a survey of Latin American
children suggested that less than 15% consumed the recommended intake of
fruits and vegetables (40). It is not possible to relate servings of fruits and
vegetables to an exact amount of vitamin C, but the WHO dietary goal of
400g/day (41), aimed at providing sufficient vitamin C to meet the 1970
FAO/WHO guidelines—that is, approximately 20–30mg/day—and lower
the risk of chronic disease. The WHO goal has been roughly translated into
the recommendation of five portions of fruits and vegetables per day (42).
Reports from India show that the available supply of vitamin C is
43mg/capita/day, and in the different states of India it ranges from 27 to
66mg/day. In one study, low-income children consumed as little as 8.2mg/day
of vitamin C in contrast to a well-to-do group of children where the intake
was 35.4mg/day (43). Other studies done in developing countries found
plasma vitamin C concentrations lower than those reported for developed
countries, for example, 20–27mmol/l for apparently healthy adolescent boys
and girls in China and 3–54mmol/l (median, 14mmol/l) for similarly aged
Gambian nurses (44, 45), although values obtained in a group of adults from
a rural district in northern Thailand were quite acceptable (median, 44mmol/l;
range, 17–118mmol/l) (46). However, it is difficult to assess the extent to
which subclinical infections are lowering the plasma vitamin C concentrations
seen in such countries.</pre>