Table 2

Nitrate knowledge in the overall cohort and when stratified by participant qualification status

Question	Overall (%)	Highest qualification (%)			P value
Question	Overall (%)	≤BSc	MSc	PhD
Health and performance effects of dietary inorganic nitrate
1. Have you heard of inorganic nitrate?*					0.001
Yes	71	41	78	86
No	14	31	10	2.8
Unsure	15	28	12	11
2. In your opinion, is dietary inorganic nitrate a primarily beneficial or harmful nutritional component?					0.002
Beneficial	51	28	63	53
Harmful	9	10	3	17
Unsure	35	59	32	19
Other	5	3	2	11
3. For each of the following variables, please specify if it is increased or decreased by dietary inorganic nitrate:
Sports performance*					0.017
Increase	59	35	71	64
Decrease	7	14	5	3
Unsure	34	52	24	33
Blood pressure*					0.016
Increase	10	7	17	0
Decrease	54	41	53	69
Unsure	36	52	31	31
Glucose levels					0.409
Increase	5	3	9	0
Decrease	17	21	15	17
Unsure	78	76	76	83
Lung function					0.179
Increase	23	21	28	17
Decrease	4	10	3	0
Unsure	73	69	69	83
Cancer risk					0.697
Increase	18	17	14	26
Decrease	12	14	12	11
Unsure	70	69	74	63
Cognitive function					0.113
Increase	27	11	37	22
Decrease	2	4	2	3
Unsure	71	86	61	75
Kidney function					0.619
Increase	13	21	9	14
Decrease	7	7	7	8
Unsure	80	72	85	78
Current and recommended intake values for nitrate
4. In the general population, what is the average daily intake of dietary inorganic nitrate of an individual?*					0.017
≤10 mg/day	6	7	10	0
11–50 mg/day	10	7	17	3
51 – 200 mg /day	15	3	14	28
201–500 mg/day	3	3	5	0
501–750 mg/day	0	0	0	0
Unsure	65	79	54	69
5. Do you know what is the acceptable daily intake (ADI) of dietary inorganic nitrate?*					0.302
Currently no ADI	11	14	13	6
0.2 mg/kg body mass/day	2	3	0	3
3.7 mg/kg body mass/day	21	7	24	28
14.8 mg/kg body mass/day	2	3	2	0
29.6 mg/kg body mass/day	1	3	0	0
Unsure	64	69	61	64
6. In your opinion, does the ADI for dietary inorganic nitrate require revision?					0.828
Yes—it should be higher	15	10	15	18
Yes—it should be lower	2	3	2	3
No	3	0	3	6
Unsure	80	86	80	74
Dietary sources of inorganic nitrate
7. For the following foods, do you think they typically have a low (<50 mg/100 g fresh-weight) or high (>100 mg/100 g fresh-weight) dietary inorganic nitrate content?
Spinach*					0.094
High	70	55	74	78
Low	11	10	9	14
Unsure	19	35	17	8
Sausage*					0.087
High	30	28	22	44
Low	46	38	54	42
Unsure	23	35	24	14
Tomato*					0.131
High	14	14	20	6
Low	51	38	48	64
Unsure	35	48	32	31
Beetroot*					0.02
High	69	45	76	81
Low	12	21	9	8
Unsure	19	35	16	11
Chocolate*					0.109
High	16	10	22	8
Low	43	38	36	58
Unsure	41	52	41	33
Bacon*					0.19
High	35	31	27	49
Low	42	38	51	31
Unsure	23	31	22	20
Lettuce*					0.362
High	42	31	43	50
Low	33	31	33	33
Unsure	25	38	24	17
Radish*					0.189
High	52	35	55	64
Low	20	24	19	17
Unsure	27	41	26	19
8. Which of the following factors do you think modify the inorganic nitrate content of food?
Cooking*					0.332
Yes	59	46	68	53
No	8	11	7	8
Unsure	33	43	25	39
Season*					0.203
Yes	58	54	54	69
No	13	7	20	8
Unsure	28	39	27	22
Soil conditions*					0.05
Yes	79	64	80	89
No	1	0	0	3
Unsure	20	36	20	8
Use of fertiliser*					0.176
Yes	71	57	72	78
No	4	4	7	0
Unsure	25	39	21	22
Storage conditions*					0.698
Yes	47	39	50	47
No	18	14	20	19
Unsure	35	46	30	33
Pickling*					0.171
Yes	41	29	51	34
No	14	11	12	20
Unsure	45	61	37	46
9. How much dietary inorganic nitrate is there, on average, in drinking water?*					0.711
< 50 mg/L	40	35	44	39
51–100 mg/L	4	7	2	6
101–200 mg/L	0	0	0	0
201–300 mg/L	0	0	0	0
Unsure	56	59	54	56
Methods of evaluating inorganic nitrate intake
10. Which biomarker would you choose to evaluate dietary inorganic nitrate intake?					0.155
Urinary nitrate	32	31	36	28
Salivary nitrite	5	7	5	3
Plasma nitrite	27	17	34	25
Exhaled nitric oxide	7	3	5	14
Unsure	27	41	20	25
Other	2	0	0	6
Nitrate metabolism
11. In the body, which of the following compounds is dietary inorganic nitrate converted into?*†					<0.001
0 point	23	41	22	9
1 point	65	59	71	60
2 points	12	0	7	31
12. Which one of these mechanisms is involved in the conversion of nitrate into nitrite in the mouth?*					0.012
C reactive protein	2	3	2	3
Oxyhaemoglobin	2	0	5	0
Salivary Amylase	19	14	27	11
Bacterial reductases	36	21	31	58
Unsure	40	62	36	28

≤BSc=highest qualification is an undergraduate degree or below, MSc=Highest qualification is a master’s degree or equivalent, PhD=highest qualification is a PhD or equivalent. Italicised answers are those identified as correct and awarded a point on the Nitrate Knowledge Index. For question 3, only sports performance and blood pressure were included in the Nitrate Knowledge Index, as evidence was deemed to be ambiguous for other physiological effects. All other questions (2, 6 and 10) were viewed as reflecting beliefs rather than knowledge ofinorganic nitrate.
*Questions which were included in the construction of the Nitrate Knowledge Index (ie, those where clear evidence exists for a correct answer).
†Potential answers were nitric oxide, nitrosamines, nitroglycerine, carbon dioxide, adrenaline, glucose and unsure. Correct answers were nitric oxide and nitrosamines. If participants identified correct and incorrect answers, their score was capped to 1 point.