An increasing proportion of the population is not covered by the current RDA for vitamin C – interrogation of EPIC-Norfolk and NHANES 2017/2018 cohorts

Figures & data

Figure 1. Participant eligibility for the final EPIC-Norfolk cohort.

Figure 2. Participant eligibility for the final NHANES 2017–2018 cohort.

Table 1. Characteristics of the EPIC and NHANES cohorts.

	EPIC cohort			NHANES cohort
Characteristics	Total cohort (n = 18185)	Females (n = 9739)	Males (n = 8446)	Total cohort (n = 2027)	Females (n = 1070)	Males (n = 957)
Age (years)	59 (51, 67)^a	59 (51, 67)^a	60 (52, 68)^b	49 (32, 63)^b	49 (32, 62)^a	50 (32, 64)^a
Sex: female male	9739 (54)^a 8446 (46)^a	9739 (100)^a 0 (0)^a	0 (0)^b 8446 (100)^b	1070 (53)^a 957 (47)^a	1070 (100)^a 0 (0)^a	0 (0)^b 957 (47)^b
Former smoker	8781 (48)^a	3522 (36)^a	5259 (62)^b	540 (27)^b	205 (19)^a	335 (35)^b
Weight (kg)	73 (64, 82)^a	66 (60, 74)^a	80 (73, 87)^b	80 (69, 96)^b	75 (63, 91)^a	86 (75, 100)^b
BMI (kg/m^2)	26 (24, 28)^a	26 (23, 28)^a	26 (24, 28)^b	29 (25, 34)^b	29 (25, 36)^a	29 (25, 33)^b
Vitamin C intake (mg/d)	79 (54, 115)^a	82 (56, 117)^a	76 (52, 112)^b	59 (27, 106)^b	56 (27, 103)^a	62 (27, 113)^b
Plasma/serum vitamin C (µmol/L)	54 (42, 65)^a	59 (48, 70)^a	48 (36, 59)^b	45 (28, 62)^b	49 (32, 65)^a	41 (24, 57)^b

Data represent median (Q1, Q2) or n (%). For the total cohorts, different superscript letters indicate p < 0.0001. For the gender subgroups, different superscript letters indicate p < 0.05 for females vs males within each cohort.

Figure 3. Correlations of weight with vitamin C intake and status in the EPIC and NHANES cohorts. (a) Intake data from EPIC cohort (green line; n = 18185; slope = -0.04) and NHANES cohort (blue line; n = 2027; slope = 0.14). (b) Plasma/serum data from EPIC cohort (green line; n = 18185; slope -0.35) and NHANES cohort (blue line; n = 2027; slope = -0.26). (c) EPIC data from high intake tertile (green line; n = 6056; slope = -0.38), medium intake tertile (orange line; n = 6071; slope = -0.35) and low intake tertile (red line; n = 6058; slope = -0.31). The slopes of the high and low intake tertiles were significantly different (p = 0.005). (d) NHANES data from higher intake category (green line; n = 675; slope = -0.27) and lower intake category (red line; n = 676; slope = -0.22). The slopes were not statistically different (p = 0.2). Lines indicate Pearson linear correlation with 95% confidence intervals indicated by dotted lines. An ‘adequate’ vitamin C concentration of 50 µmol/L is indicated by the horizontal dashed line.

Table 2. Characteristics of vitamin C intake categories in the EPIC and NHANES cohorts.

	EPIC cohort^1			NHANES cohort^2
Characteristics	Lower intake (n = 6058)	Medium intake (n = 6071)	Higher intake (n = 6056)	Lower intake (n = 1014)	Higher intake (n = 1013)
Age	60 (51, 68)^a	59 (51, 67)^a	59 (52, 67)^a	48 (29, 63)^a	50 (34, 63)^a
Sex: female male	3016 (50)^a 3042 (50)^a	3317 (55)^b 2754 (45)^b	3406 (56)^b 2650 (44)^b	556 (55)^a 458 (45)^a	514 (51)^a 499 (49)^a
Former smoker	3144 (52)^a	2856 (47)^b	2781 (46)^b	287 (28)^a	253 (25)^a
Weight (kg)	73 (65, 83)^a	72 (64, 83)^b	73 (64, 82)^ab	81 (69, 98)^a	80 (68, 95)^b
BMI (kg/m^2)	26 (24, 29)^a	26 (24, 28)^b	26 (24, 28)^b	30 (25, 35)^a	29 (25, 34)^b
Vitamin C intake (mg/d)	45 (36, 54)^a	79 (70, 89)^b	133 (115, 164)^c	27 (16, 41)^a	106 (79, 152)^b
Plasma vitamin C (µmol/L)	44 (30, 56)^a	54 (44, 64)^b	61 (52, 71)^c	36 (20, 53)^a	53 (40, 67)^b

Data represent median (Q1, Q2) or n (%).

¹ EPIC cohort: tertiles were derived from 7-day food diaries. Intake category boundaries were: lower ≤61.5 mg/d, medium 61.6–100.2 mg/d, higher ≥100.3 mg/d.

² NHANES cohort: 50 percentiles were derived from 24-h recalls. Intake category boundaries were: lower ≤58.3 mg/d, higher ≥58.4 mg/d. Different superscript letters indicate p < 0.05 within each cohort.

Figure 4. Proportion of participants reaching (green bars)/not reaching (red bars) adequate vitamin C status at different weights in the EPIC (a) and NHANES (b) cohorts. The mean (SD) weight and vitamin C intake for the EPIC cohort was 73 (64, 82) kg and 79 (54, 115) mg/d; and for the NHANES cohort was 80 (69, 96) kg and 59 (27, 106) mg/d. Upper dashed line indicates 97.5% and middle dashed line indicates 50% of the participants.

Figure 5. Vitamin C dietary intake versus plasma concentration curves in the EPIC cohort. (a) Intake versus concentration curve for total EPIC cohort (n = 18185). (b) Intake versus concentration curves for lighter weight tertile (green line; n = 6028), medium weight tertile (orange line; n = 6090) and heavier weight tertile (red line; n = 6067). (c) intake versus concentration curves for females (lighter weight tertile; green; n = 3287 vs heavier weight tertile; red; n = 3295) and (d) males (lighter weight tertile; green; n = 2812 vs heavier weight tertile; red; n = 2848). Sigmoidal (four parameter logistic) curves with asymmetrical 95% confidence intervals were fitted to dose-concentration data to estimate the vitamin C intakes required to reach ‘adequate’ serum vitamin C concentrations of 50 μmol/L (dashed line).

Table 3. Characteristics of weight tertiles in the EPIC and NHANES cohorts.

	EPIC cohort			NHANES cohort
Characteristics	Lighter weight (n = 6028)	Medium weight (n = 6090)	Heavier weight (n = 6067)	Lighter weight (n = 677)	Medium weight (n = 675)	Heavier weight (n = 675)
Age (years)	59 (50, 68)^a	60 (52, 68)^b	59 (52, 66)^ac	45 (28, 64)^a	53 (34, 63)^b	49 (33, 62)^ab
Sex: female male	5209 (86)^a 819 (14)^a	2963 (49)^b 3127 (51)^b	1567 (26)^c 4500 (72)^c	481 (71)^a 196 (29)^a	309 (46)^b 366 (54)^b	280 (41)^b 395 (59)^c
Former smokers	2195 (36)^a	3013 (49)^b	3573 (59)^c	127 (19)^a	184 (27)^b	229 (34)^c
Weight (kg)	61 (57, 64)^a	73 (70, 76)^b	86 (82, 92)^c	64 (57, 69)^a	80 (77, 85)^b	104 (96, 117)^c
BMI (kg/m^2)	23 (22, 25)^a	26 (25, 28)^b	29 (27, 32)^c	24 (22, 26)^a	29 (27, 32)^b	36 (33, 41)^c
Vitamin C intake (mg/d)	80 (55, 116)^a	80 (54, 114)^ab	77 (52, 114)^b	62 (30, 110)^a	62 (28, 105)^ab	52 (24, 102)^b
Plasma vitamin C (µmol/L)	60 (48, 70)^a	54 (42, 65)^b	48 (36, 59)^c	54 (35, 68)^a	46 (31, 61)^b	39 (21, 54)^c

Data represent median (Q1, Q2) or n (%). EPIC weight category boundaries were: lighter ≤67.3 kg, medium 67.4–78.6 kg, heavier ≥78.7 kg. NHANES weight category boundaries were: lighter ≤72.3 kg, medium 72.4–90.2 kg, heavier ≥90.3 kg. Different superscript letters indicate p < 0.05 within each cohort.

Figure 6. Proportion of participants in the EPIC and NHANES cohorts reaching adequate vitamin C concentrations at different dietary intake categories. The mean (SD) intake for the (a) total EPIC cohort (green bars) was 89 (50) mg/d and total NHANES cohort (blue bars) was 79 (77) mg/d, (b) EPIC females was 92 (50) mg/d and NHANES females was 74 (66) mg/d, (c) EPIC males was 88 (51) mg/d and NHANES males was 85 (87) mg/d. Upper dashed line indicates 97.5% and middle dashed line indicates 50% of the participants.

Table 4. Proportion of nonsmoking men and women of the EPIC-Norfolk and NHANES 2017–2018 cohorts reaching ‘adequate’ plasma concentration of 50 µmol/L based on the ingestion of the RDA from UK (40 mg/d) or USA (75/90 mg/d for women, men).

	EPIC-Norfolk (UK) (n = 18185)	NHANES 2017–2018 (USA) (n = 2027)
Proportion (%) achieving adequate plasma status consuming the RDA ± 10%	35 % (46% women, 24% men)	50% (57% women, 43% men)
Proportion (%) achieving adequate plasma status consuming ≥ RDA of vitamin C	64% (76% women, 51% men)	62% (67% women, 56% men)

Data availability statement

NHANES 2017–2018 data are publicly available at https://www.cdc.gov/nchs/nhanes/index.htm.

EPIC-Norfolk data are available by request through https://www.epic-norfolk.org.uk/forresearchers/data-sharing/data-requests