The betaine content of New Zealand foods and estimated intake in the New Zealand diet

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JOURNAL OF FOOD COMPOSITION AND ANALYSIS

Journal of Food Composition and Analysis 18 (2005) 473–485 www.elsevier.com/locate/jfca

Original Article

The betaine content of New Zealand foods and estimated intake in the New Zealand diet Sandy Slowa,*, Marisa Donaggioa, Peter J. Cresseyb, Michael Levera, Peter M. Georgea, Stephen T. Chambersc a

b

Biochemistry Unit, Canterbury Health Laboratories, P.O. Box 151, Christchurch 8000 New Zealand Food Safety Program, Institute of Environmental Science and Research, 27 Creyke Road, Christchurch 4, New Zealand c Department of Infectious Diseases, Christchurch Hospital, New Zealand Received 19 November 2003; received in revised form 19 April 2004; accepted 19 May 2004

Abstract We have measured the glycine betaine, proline betaine, trigonelline and dimethylsulphoniopropionate (DMSP) content of 74 predominantly processed foods. Combining these data with a previous survey (predominantly commodity based) and using data from the New Zealand National Nutrition Survey, the betaine intake in the average New Zealand diet has been estimated. Typically, glycine betaine was primarily found at high levels (X150 mg/g) in grain products (bread, pasta, flour), while proline betaine was found in fruit, especially oranges and orange juice and trigonelline was found in coffee. DMSP was only found in very small quantities (o10 mg/g) in a small number of foods. Different sources of individual foods showed variation in betaine content and some food processing, particularly canning, affected betaine content, with betaine found in both the liquid and solid portions of the canned products. The mean intake (7sem) of glycine betaine, proline betaine and trigonelline in the average New Zealand diet was estimated at 29874, 4772 and 11973 mg/day, respectively. Generally, men had higher betaine intakes than females and intake decreased with age. r 2004 Elsevier Inc. All rights reserved. Keywords: Glycine betaine; Proline betaine; Trigonelline; Dimethylsulphoniopropionate; DMSP; Dietary intake; Homocysteine; BHMT

*Corresponding author. Tel.: +64-3-364-0319; fax: +64-3-364-0750. E-mail address: [email protected] (S. Slow). 0889-1575/$ - see front matter r 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.jfca.2004.05.004

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1. Introduction In mammals, glycine betaine (N,N,N-trimethylglycine) has dual roles. Firstly, it is an osmolyte, preserving osmotic equilibrium and maintaining the tertiary structure of macromolecules in the kidney (Yancey and Somero, 1979; Yancey and Burg, 1990) and other tissues (Zhang et al., 1996; Weik et al., 1998). Secondly, it is a methyl group donor, required for the formation of methionine and S-adenosylmethionine (SAM) (Lever et al., 2004; Barak et al., 1996). In humans, glycine betaine is obtained through dietary intake or endogenously synthesized by a two-step oxidation of choline (Flower et al., 1972). The glycine betaine concentration of human plasma is highly regulated (Lever et al., 2004) and it is almost completely resorbed in the kidney (Lever et al., 1994), probably via various amino acid and carnitine transporters that have broad specificity (Stevens and Wright, 1985; Wunz and Wright, 1993; Wagner et al., 2000). Plasma glycine betaine concentrations are lower in patients with renal disease (Lever et al., 1994), and urinary excretion is higher in patients with diabetes mellitus (Dellow et al., 1999). Various glycine betaine analogues are found in plants and other organisms. High levels (up to 100 mmol/g dry mass) of proline betaine (stachydrine) can be found in some citrus varieties (Nolte et al., 1997; de Zwart et al., 2003), while trigonelline is a natural constituent of coffee beans (Mazzafera, 1991), tomatoes (Rajasekaran et al., 2001) and alfalfa (Tramontano and Jouve, 1997). Dimethylsulphoniopropionate (DMSP), a sulfonium analogue, is found in marine bacteria and phytoplankton and consequently filter feeders and marine animals accumulate it (Blunden and Gordon, 1986). Proline betaine has been detected in human plasma and urine samples (Lever et al., 1994) and the source of these various glycine betaine analogues is believed to be dietary. Unlike glycine betaine, however, these analogues are not accumulated in the kidney (Lever et al., 1994; Randall et al., 1996). In a reaction catalysed by betaine homocysteine methyltransferase (BHMT; E.C. 2.1.1.5) a methyl group is transferred from glycine betaine to homocysteine, producing methionine and N,N-dimethylglycine (reviewed Malinow, 1994). Homocysteine is derived through the metabolism of methionine and mildly elevated plasma concentrations have been associated with increased risk of cardiovascular, cerebral and peripheral vascular disease (reviewed Welch and Loscalzo, 1998; Boushey et al., 1995). Elevated plasma homocysteine concentrations have also been implicated in the development of birth defects and dementia and Alzheimer’s disease (Seshadri et al., 2002). Glycine betaine supplementation has been a successful therapy for lowering circulating homocysteine levels in homocystinuria (Wilcken et al., 1983) and in chronic renal failure patients following a methionine load (Mcgregor et al., 2002), as well as in healthy subjects (Brouwer et al., 2000). Studies with purified enzyme have shown that proline betaine (Mulligan et al., 1998) and DMSP (Goeger and Ganther, 1993; Garrow, 1996) are also BHMT substrates, and these may either inhibit glycine betaine demethylation, or act as substrates in homocysteine metabolism. Although glycine betaine supplementation has proven useful for lowering plasma homocysteine concentrations, it is expensive and diarrhoea has been reported during therapy (Knopman and Patterson, 2001). Another means of moderating plasma homocysteine concentration may be to increase the dietary intake of foods known to be high in glycine betaine and other substrates of BHMT. However, before this can be implemented it is necessary to determine the betaine content of foods consumed in a normal diet.

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In a previous study, we surveyed the betaine content of a range of foods (de Zwart et al., 2003). The only betaines found at X150 mg/g were glycine betaine, proline betaine, trigonelline and DMSP. Different sources of individual foods showed variation in betaine content and the way in which individual foods were cooked affected betaine content, with boiling causing the highest loss (de Zwart et al., 2003). A limitation of the study, however, was that the foods surveyed were primarily commodities, the effect of various food processing on betaine content was unknown. In this study we have extended the initial survey and measured the betaine content (glycine betaine, proline betaine, trigonelline and DMSP) of a range of processed foods. Combining the data from both food surveys and data from the New Zealand National Nutrition Survey (Russell et al., 1999) the betaine intake in the New Zealand diet has been estimated.

2. Materials and methods 2.1. Sampling and reagents The foods included in this survey consisted of 74 products commonly available and consumed in New Zealand (Table 1). Foods were purchased from local supermarkets and two different brands per product were examined, with the exception of a small number of foods where two brand varieties were not commonly available. Where possible, one of the brands analysed was a cheaper plain packaged brand. For convenience the different products were grouped into 10 food categories: grains, fruit, vegetables, beverages-non alcoholic, beverages-alcoholic, meat, seafood, dairy products, nuts and miscellaneous. These food groups are based on those used for the New Zealand Total Diet Survey (Cressey et al., 2000; Vannoort et al., 2000), however, the oils and fats, spreads and sweets and takeaways groups have been combined into ‘miscellaneous’ and the seafood has been separated from the ‘chicken, eggs, fish and meat category. The betaine content of the juice component of the canned foods was analysed separately. A small amount of fresh produce, which had not been included in the previous study (de Zwart et al., 2003), was also included in this survey (Table 1). Only the edible portion of the fresh produce was analysed. All reagents were of analytical-reagent grade. Betaine standards were prepared using bidistilled water. Glycine betaine and trigonelline were purchased from Sigma (St Louis, USA). DMSP and proline betaine (stachydrine) were synthesized as previously described (Randall et al., 1995; Samuelsson et al., 1998) (Fig. 1). 2.2. Betaine analysis All foods were pre-extracted using dichloromethane, which removes hydrophobic compounds, increases HPLC column life and has been shown not to remove betaine. The betaines were extracted from the foods as described previously (de Zwart et al., 2003) using the appropriate extraction procedure (differing for solid foods, liquid foods and fatty foods) and extracted samples were stored frozen until analysis.

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Table 1 The glycine betaine, proline betaine and trigonelline content (mg/g) of various foods Food

Grains Bread

Cereals

Biscuits Snacks Pasta

Other

Fruit Canned

Fresh

Dried

Other Vegetables Canned

Glycine betaine

Proline betaine

Trigonelline

Brand 1

Brand 2

Brand 1

Brand 2

Brand 1

Brand2

White Wholemeal Wholegrain Bran Cornflakes Muesli Wheat biscuits Chocolate Plain Extruded corn snacks Nacho chips Fettuccini (fresh) Spaghetti (canned in sauce) Noodles (instant) Cake (plain) Cracker (plain) Cracker (rice) Muffin (blueberry) Scone (cheese)

360 670 560 2300 7 270 2500 160 290 73 Trace 1400 18 1400 270 1300 6 120 440

520 790 620 7200 6 440 1900 160 430 21 11 1300 50 990 170 1000 Trace 160 500

— Trace Trace — — Trace — — — — — Trace — — — Trace — Trace

— — Trace 9 — — — — — — — — — — — — 11 — —

Trace Trace 6 7 — 42 Trace Trace Trace — 21 Trace Trace Trace — Trace — — Trace

Trace Trace Trace 29 Trace 33 6 Trace Trace — 18 Trace 7 Trace — Trace — — Trace

Apricots (fruit) Apricots (juice) Fruit salad (fruit) Fruit salad (juice) Mandarins (fruit)a Peach (fruit) Peach (juice) Pineapple (fruit) Pineapple (juice) Avocado Grapes (red) Grapes (green) Nectarines Strawberries Apricots Prunes Raisins Sultanas Apple juice Orange juice

Trace Trace — — Trace — — — — 35 Trace — — — Trace Trace Trace Trace — —

— Trace — —

— — — —

— — Trace Trace Trace Trace 11 33 13 8 — Trace Trace 17 — 16 16 Trace 20

Baked beans Capsicum (red) Capsicum (green) Capsicum (orange)

Trace Trace 24 10

47 Trace Trace —

— — — Trace 3 Trace — — Trace Trace Trace Trace Trace — —

— — — — 920 — — — — 8 Trace Trace Trace — — — — — — 700

— — — — — Trace — — — — — — — — 780

Trace Trace Trace Trace 15 Trace Trace 8 20 58 10 14 Trace Trace 11 Trace 17 12 Trace 10

Trace 12 31 11

— 6 Trace Trace

— Trace Trace Trace

51 — — —

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Table 1 (continued) Food

Fresh

Other Beverages-non alcoholic Instant Coffee Tea Soft Drink Beverages-alcoholic Wine Beer Meat Canned Fresh Cured

Other

Seafood Canned

Other Dairy products Milk

Glycine betaine

Proline betaine

Trigonelline

Brand 1

Brand 2

Brand 1

Brand 2

Brand 1

Brand2

Capsicum (yellow) Corn (kernels) Corn (juice) Corn (creamed) Tomatoes (fruit) Tomatoes (juice) Asparagus Onions Potatoes (peeled) Potatoes (unpeeled) Potato chips Tomato sauce

10 — Trace — — Trace 45 — 38 39 Trace —

26 — Trace Trace — — 33 Trace 37 26 Trace —

Trace — — — — — Trace Trace Trace Trace — Trace

trace — — — — — 7 Trace Trace Trace — Trace

— — Trace — 25 110 8 Trace 9 9 16 8

Trace Trace Trace Trace 23 110 Trace Trace 21 17 32 5

Granulated Powdered Earl grey Plain Cola Lemonadeb

31 62 120 51 — —

30 68 50 91 — —

— — — — — —

— — — — — —

11,000 14,000 — — — —

12,000 11,000 — — — —

White (chardonnay) Draught Lager

Trace 77 57

Trace 58 60

Trace — —

— — —

18 Trace 8

12 7 8

Corned beefa Mutton Bacon Ham Corned beef Chicken nuggets Meat pie (mince) Sausages (beef, uncooked)a Sausages (beef, pre-cooked)a Chicken soup (powdered)

83 180 49 95 76 140 240 320 280 71

Salmon (meat) Salmon (juice) Tuna (meat) Tuna (juice) Fish (battered)a Fish (crumbed)

23 11 33 40 71 120

20 19 45 78

Flavoured milk (chocolate) Homogenized Soy Trim

6 28 Trace 6

62 97 81 140 280 240

180

7 11 8 6 10 Trace Trace Trace Trace Trace

— Trace 6 10 Trace Trace

— 10 Trace 6 7

150

Trace Trace 8 6 — 12

Trace 7 12 11

— — — —

— — — — — Trace 6 10 7 —

— — — — 15 —

— — — — —

29

— — — — — —

— — — —

— — — —

— — 13 —

—

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Table 1 (continued) Food

Cheese

Other

Glycine betaine

Proline betaine

Trigonelline

Brand 1

Brand 2

Brand 1

Brand 2

Brand 1

Brand2

Brie Blue Edam Feta Ice cream (plain)a Ice cream (chocolate)a

54 33 Trace Trace Trace Trace

67 35 Trace Trace

110 31 7 — — —

260 65 — —

— — — — — —

— — — —

Peanut butter (smooth)

10

9

—

—

—

—

Jam (strawberry) Marmalade (sweet orange)

— —

— —

12 49

32 30

— —

— —

Nuts Miscellaneous Spreads

Data for each brand are means of triplicate determinations. Foods highlighted in bold contained high levels (X150 mg/ g) of one or more of the betaines. —Levels below 1 mg/g; trace=betaine content between 1 and 5 mg/g. The betaine content of liquids are expressed as mg/ mL. a One brand analysed. b Lemon flavoured drink, not made using real lemons.

Fig. 1. Chemical structures of the betaines measured in this study. Trivial names are written under each structure.

The extracts were derivatized with 2-naphthacyl trifluoromethanesulphonate (Happer et al., 2004) based on the method of Lever et al. (1992). Betaine analysis was performed by HPLC (SIL-10AD VP, Shimadzu, Japan) with separation using an Alusphere 250
4 mm alumina column (Merck, Darmstadt, Germany) as the stationary phase. A mobile phase consisting of 1 mm succinic acid; 3.6 mm triethylamine buffer, 4.5% water in acetonitrile was used. The flow rate was 1 mL/min and sample run time was 60 min. The column temperature was maintained at 40 C and

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the sample injection volume was 100 mL. The HPLC eluates were monitored at 249 nm and the chromatograms collected and integrated using Delta for Windows version 5 (DataworX Pty Ltd; Brisbane, Australia). The concentration of the various betaines was quantified by comparing to external standards. Each extract was analysed in triplicate within the same run and the mean betaine concentration has been reported (mg/g or mg/mL). 2.3. Dietary modelling The 1997 New Zealand National Nutrition Survey (NNS97) was a voluntary cross-sectional population survey, which included 24 h dietary recall (24 HDR) interviews with 4636 subjects (Russell et al., 1999). Data were collected over a 12 month period. A mapping exercise was carried out to match the foods for which betaine content information was available from the current study or from de Zwart et al. (2003) to the approximately 4000 different food descriptors present in the NNS97 24 HDR records. This mapping process assumes that a single food can be taken as representative of the betaine content of a wider range of related or similar foods. For example, ‘canned apricots were taken to represent all forms of apricot including fresh apricots, canned apricots, and apricot sauces. Where betaine content data were available on different forms of the same food (e.g. fresh beetroot and canned beetroot), these were mapped separately. Following mapping, the 24 HDR record food amounts were multiplied by betaine concentration data and summed for each of the 4636 respondents in the NNS97 to give 4636 estimates of betaine dietary intake. All manipulations were carried out using Microsoft FoxPro. 2.4. Daily betaine intake by food group The overall contribution of each of the ten food groups (grains, fruit, vegetables, beverages-non alcoholic, beverages-alcoholic, meat, seafood, dairy, nuts and miscellaneous) to total betaine intake was calculated by summing the contributions for each member of the food group across all respondents. 2.5. Demographic analysis of betaine intake The NNS97 also captured demographic information on all respondents. This was used to segment the 4636 estimates of betaine intake by age and gender. For each segment the mean level of betaine intake was calculated and the associated standard error of the mean. 2.6. Statistical analyses Linear regression was used to determine the significance of increasing age on betaine intake for both males and females and t-tests were used to examine the significance of gender on betaine intake. Significance was tested at the P ¼ 0:05 level using SigmaStat 2 for Windows, standard version (SPSS Inc., Chicago, IL, USA).

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3. Results and discussion 3.1. Betaine content The betaine content of the various products has been reported corrected for recovery. The coefficient of variation for foods containing high levels of betaine (X150 mg/g) was 9.6%, while those foods that contained moderate to small levels of betaine (range 5–150 mg/g) the coefficient of variation was 15.3%. Of the four betaines analysed, DMSP was only detected in a small number of products (canned fish and cured meats) with the highest levels being detected in the juice from canned salmon (9 mg/mL). This is consistent with our previous findings (de Zwart et al., 2003). As a result of the small quantities of DMSP, a normal diet would be likely to contain only low levels and thus DMSP intake has not been included in the dietary analysis. Table 1 shows the glycine betaine, proline betaine and trigonelline contents of the foods that were analysed in this study. Foods that are shown in bold contained high levels (X150 mg/g) of one or more of glycine betaine, proline betaine or trigonelline. Glycine betaine was found at high levels in most products that contained grains or flour (bread, biscuits, some cereals, battered and crumbed products) and is consistent with the findings of Zeisel et al. (2003), where similar products were also shown to have glycine betaine present. Proline betaine was found at high levels in citrus-based products (orange juice and canned mandarins) and some cheeses (brie). Trigonelline was only found at high levels in instant coffee (powdered and granulated), although small to moderate levels (between 10 and 150 mg/g) were detected in a number of fruit and vegetables, both canned and fresh (tomatoes, potatoes, mandarins, baked beans). The two different brands of the same product showed some variation in betaine content and in some instances the difference was quite marked (bran cereal, plain biscuits, brie cheese and chicken nuggets). In addition, the values we obtained for the glycine betaine content in some of the foods was lower (although in the same order of magnitude) than that determined by Zeisel et al. (2003). This variability in betaine content is not surprising because of their osmoprotectant and cryoprotectant functions. The level of betaine would be expected to be dependent on the stress level of the crop. For example, grain grown during a drought would be expected to have higher betaine levels compared with crops grown on well-irrigated fields. Similarly, trigonelline has been found to increase in alfalfa (Tramontano and Jouve, 1997) and tomatoes (Rajasekaran et al., 2001) under salt stress. Nevertheless, the betaines that were detected in one brand of a foodstuff were also detected in the second brand, and the same foods were found to have high levels of glycine betaine by Zeisel et al. (2003). Overall the betaine content of the juice of the canned products was similar to that of the solid food, suggesting that the betaines were released from the solid to the liquid portion during processing. As betaines are small highly water-soluble molecules this was expected. It is also consistent with our previous findings where various cooking methods were found to affect betaine content with boiling causing significant losses (up to 80%) of betaine from food (de Zwart et al., 2003). 3.2. Estimated dietary intakes of betaines Table 2 gives the overall means and 5th–99th percentile estimated daily dietary intakes for glycine betaine, proline betaine and trigonelline. The mean daily dietary intakes (7sem)

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Table 2 Mean and percentile dietary intakes (mg/day) for three betaines (glycine betaine, proline betaine and trigonelline), based on 1997 NNS and the current study (n ¼ 4636) Percentile Betaine

Mean

5

25

50

75

95

99

Glycine betaine Proline betaine Trigonelline

298 47 119

66 0.2 2.0

141 0.6 10

227 1.3 62

351 20 159

789 260 403

1363 665 756

Table 3 Mean betaine intake (mg/day) for three betaines (glycine betaine, proline betaine and trigonelline) by food group, based on 1997 NNS and current study Mean betaine intake (mg/day) (percentage of total) Food group

Glycine betaine

Proline betaine

Trigonelline

Beverages, alcoholic Beverages, non-alcoholic Dairy Fruits Grains Meat Nuts Seafood Vegetables Miscellaneous Total

10(3) 34(11) 3(1) o1(o1) 198(67) 33(11) o1(o1) 6(2) 13(4) o1(o1) 298(1 0 0)

o1(o1) o1(o1) o1(o1) 45(97) o1(o1) o1(o1) o1(o1) o1(o1) o1(1) o1(o1) 47(1 0 0)

2(1) 104(87) o1(o1) 2(2) 6(5) o1(o1) o1(o1) o1(o1) 5(4) o1(o1) 119(1 0 0)

for glycine betaine, proline betaine and trigonelline, respectively, are 29874, 4772, and 11973 mg/day. Dietary intakes of nutrients and contaminants often conform to an approximately log-normal distribution and the distribution of estimated daily dietary intakes for betaines approximate to this distribution, although the best fit for the distribution of glycine betaine intakes is to the log logistic distribution. No previous estimates of the dietary intake of betaines could be located. Normal dietary intakes, as shown in Table 2, are one-to-two orders of magnitude lower than levels administered during clinical trials (Brouwer et al., 2000; Knopman and Patterson, 2001; Schwab et al., 2002). 3.3. Major contributors to dietary betaine intake Table 3 shows the contributions of each of 10 food groups to estimated mean dietary betaine intake. For each of the three betaines intake is dominated by a single food group, with a different food group dominating in each case. Dietary intake of glycine betaine is dominated by grain products (67% of total intake), with bread contributing approximately one-third of the total dietary betaine intake. Significant

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non-grain contributors to glycine betaine intake include tea, beer and meat pies, although the contribution from meat pies will be largely due to the cereal content of the pie casing. Dietary intake of proline betaine is almost entirely due to fruit consumption (97% of total intake), with oranges and orange juice contributing over 96% of total dietary intake of proline betaine. Dietary intake of trigonelline is dominated by consumption of beverages (87% of total intake). The contribution of beverages to total dietary trigonelline intake is almost entirely due to the presence of this betaine in coffee. Rolled oats and potatoes also contribute to dietary trigonelline intake. 3.4. Variations in dietary betaine intake due to age/gender The mean daily intakes of glycine betaine, proline betaine and trigonelline (mg/day) for various age/gender groups are shown in Table 4. Betaine intake for males is significantly higher than Table 4 Mean dietary intakes (mg/day) for three betaines (glycine betaine, proline betaine and trigonelline) for various age/ gender groups, based on 1997 NNS and the current study Mean betaine intake (mg/day) (standard error of the mean) Group

n

Glycine betaine

Proline betaine

Trigonelline

15–18 year, male

109

19–24 year, male

145

25–44 year, male

759

45–64 year, male

588

65+ year, male

326

15+, male

1927

15–18 year, female

137

19–24 year, female

209

25–44 year, female

1205

45–64 year, female

667

65+ year, female

491

15+, female

2709

15+, total population

4636

382 (47) 406 (31) 386 (12) 349 (12) 281 (9) 358 (7) 253 (22) 251 (17) 273 (8) 238 (7) 233 (8) 255 (4) 298 (4)

101 (22) 115 (20) 53 (5) 35 (4) 23 (4) 50 (3) 79 (14) 73 (14) 48 (4) 35 (3) 29 (3) 45 (2) 47 (2)

61 (11) 118 (17) 155 (7) 135 (6) 101 (7) 132 (4) 52 (7) 105 (11) 124 (5) 122 (10) 74 (4) 110 (4) 119 (3)

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females (Po0:001) with the exception of proline betaine where there are no significant differences in intake between gender within any age group. Glycine betaine intake significantly decreases with age from 25–44 years to 65+ years in males (P ¼ 0:028), while it is not significantly different (P ¼ 0:234) as age increases in females. Proline betaine intake significantly decreases as age increases for males (P ¼ 0:026) and females (P ¼ 0:012), while trigonelline intakes are not significantly different for either gender as age increases (Table 4). Plasma homocysteine concentrations increase with age, a consequence of many factors such as renal dysfunction and malabsorption of micronutrients (folate, vitamin B12 and B6) (Joosten et al., 1993; Selhub et al., 2000). Mildly elevated homocysteine has been associated with neurocognitive decline (dementia and Alzheimer’s’ disease) in older populations (Seshadri et al., 2002; Nourhashe! mi et al., 2000). In males, lower intakes of glycine betaine with increasing age may also be a contributing factor in raising plasma homocysteine concentrations. It may therefore be beneficial, particularly for older males, to improve glycine betaine intake by increasing consumption of foods that are high in glycine betaine. Although we have estimated the betaine content of the average diet, some special diets are likely to exclude major sources of betaine. For example, patients with coeliac disease, because of the lack of wheat products in their diet, are likely to have a lower than average intake of glycine betaine, whilst vegetarians may have a higher than average intake of trigonelline because they generally consume higher amounts of legumes (chickpeas and lentils). Whilst the effects of proline betaine and trigonelline in humans are unknown, a previous study, where high levels (E500 mg/ kg) of proline betaine and trigonelline were administered to rats, showed that proline betaine and to a lesser extent, trigonelline, significantly increased plasma homocysteine concentration (Slow et al., 2004). If the same is true for humans, decreasing proline betaine and trigonelline intake, while increasing glycine betaine intake may prove beneficial, particularly if plasma homocysteine is already mildly elevated. Nevertheless, whether glycine betaine concentrations can be raised sufficiently by dietary manipulation to assist in lowering plasma homocysteine is unproven.

4. Conclusion The levels of glycine betaine, proline betaine and trigonelline in the average New Zealand diet can be attributed to a small number of foods, with each food type tending to have only one betaine present at high levels (X150 mg/g). The main source of glycine betaine in the average New Zealand diet is from grain products (67% of total intake), whilst proline betaine comes from fruit (97% provided by oranges and orange juice) and trigonelline from coffee (87%). The levels of betaine in the diet can vary widely, depending on the source of the food and the way in which the food is processed and/or cooked. A large proportion (over 50% in some cases) of the betaine content can be found in the liquid portion of canned products, presumably a result of betaines being released from the solid portion into the liquid during the canning process. Glycine betaine intake could be increased through dietary manipulation, where it would be relatively simple to consume 500 mg/day of glycine betaine. A further 500 mg/day of glycine betaine may also be supplied through the oxidation of choline (Zeisel and Blusztajn, 1994). However, whether an intake at this level would be effective at lowering plasma homocysteine and improving human health is unknown.

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Acknowledgements We acknowledge support from the Health Research Council of New Zealand. Some of the equipment used in the analytical work was provided with assistance from the New Zealand Lottery Grants Board.

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