Occurrence of Low Intakes and Poor Biochemical Status in Present Day Societies

Although scurvy is rare, biochemical evidence of poor vitamin C status is not uncommon in certain high-risk groups in different human populations. Studies in The Gambia in West Africa, for instance, have shown that there is a regular seasonal cycle of availability of foods rich in vitamin C, with a good availability in the dry season alternating with a severe shortage during the rainy season. Plasma, buffy-coat, and breast-milk concentrations are all, on average, adequate in the dry season but are severely reduced during the rains. Functional and health-related parameters also deteriorate during the rains, but it has so far proved difficult to reverse this deterioration by vitamin C supplements alone. Therefore, robust evidence of health consequences of this seasonal availability cycle has not yet been obtained.

From recent surveys in the UK, Table 3 shows the prevalence of low intakes of vitamin C (estimated from the proportion of participants receiving less than the lower reference nutrient intake (LRNI), which is the amount deemed to be sufficient for only a few people in a population group, namely the 2.5% with the lowest requirements). Also shown in Table 3 is the prevalence of plasma concentrations below the lower cut-off of normality, set at 0.2mgdl_1 or 11 mmoll-1. This is shown for several subgroups of the British population of different ages, from data collected in three nationally representative population surveys during the decade 1990s. It is clear from these results that very few people were getting less than the LRNI for vitamin C over a 4 day or 7 day period of weighed-intake estimates of their diets. Low plasma levels were likewise relatively uncommon in the younger age groups; however, they were more common in older people and were especially prevalent, at almost 40%, in older people living in institutions such as nursing homes. These relatively low plasma levels seen in frail older people are likely to be caused by factors other than very low intakes of the vitamin. In the UK, unlike The Gambia, there was relatively little evidence of a major seasonal variation in vitamin C intake or status at the end of the twentieth century.

Other studies have shown that vitamin C absorption does not appear to be abnormally low in healthy older people. However, there is growing evidence that the multiple pathologies associated with old age (and with debility at any age) are associated with increased turnover of the vitamin. Older people with very low levels of vitamin C are at higher risk of dying sooner than those with high levels, although short-term vitamin supplements generally fail to reverse this increased risk. It thus appears that vitamin C status can act as a barometer of health as well as being a marker of adequacy of vitamin C intake. Further research is needed to determine the key mechanisms that affect the rate of vitamin C turnover and its control in different age

Table 3 Prevalence of low vitamin C intakes and low plasma vitamin C concentrations in Britain at the end of the twentieth century: data from the National Diet and Nutrition Surveysa

Age group

LRNb (mgday-1)

Intake less than LRNf

C Less than 11 ßmoll 1 plasma vitamin

Pre-school 1.5-4.5 years

8

8/723 = 1.1%

24/723 = 3.3%

Young people 4-18 years

4-10 years

8

1/423 = 0.2%

6/422 = 1.4%

11-14 years

9

0/307 = 0%

4/307 = 1.3%

15-18 years

10

1/271 = 0.4%

8/271 = 3.0%

Adults 65 years and over

Free-living 65-79 years

10

8/606 = 1.3%

88/606 = 14.5%

Free-living 80+ years

10

7/274 = 2.5%

45/274 = 16.4%

Institution-living

10

2/248 = 0.8%

98/248 = 39.5%

aConfined to those participants who provided both a weighed-intake record for 4 or 7 days and a blood sample for the biochemical analysis. Source: National Diet and Nutrition Survey Series, commissioned jointly by the Department of Health and MAFF, whose responsibility has since been transferred to the Food Standards Agency. The National Diet and Nutrition Survey Reports are published by The Stationery Office.

bLower reference nutrient intake, deemed to be sufficient for only 2.5% of the population who have the smallest requirements.

aConfined to those participants who provided both a weighed-intake record for 4 or 7 days and a blood sample for the biochemical analysis. Source: National Diet and Nutrition Survey Series, commissioned jointly by the Department of Health and MAFF, whose responsibility has since been transferred to the Food Standards Agency. The National Diet and Nutrition Survey Reports are published by The Stationery Office.

bLower reference nutrient intake, deemed to be sufficient for only 2.5% of the population who have the smallest requirements.

groups and different metabolic states. Since frail older people are at high risk of developing pressure sores and of needing surgery for a variety of ailments, there seems to be a potential public-health advantage in avoiding the development of very low vitamin C stores in this vulnerable age group, as a sensible precautionary measure.

See also: Antioxidants: Diet and Antioxidant Defense. Ascorbic Acid: Physiology, Dietary Sources and Requirements. Fruits and Vegetables. Nutritional Assessment: Biochemical Indices. Older People:

Nutritional-Related Problems. Supplementation: Role of Micronutrient Supplementation.

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