42 The nutrition handbook for food processors systems(Olson et al, 2000). The enzyme responsible for the conversion of retinol to hrr has not been characterised 3.6 Health-related roles of B-carotene 3.6.1 B-Carotene as an antioxidant The ability of carotenoids to act as antioxidants can be measured in vitro, ex vivo, or in vivo. LDL isolated from an individual who has been supplemented with carotenoids and then evaluated for its antioxidant activity is an extension of an in vivo study, i.e. ex vivo. However, when carotenoids are added to plasma and then the oxidisable value of the ldl is measured it is more like an in vitro model Krinsky, 2001). Many studies report using the ex vivo method of measuring the oxidisability of the Ldl particles after coning ncr reased amounts of car containing foods. However, when using fruits and vegetables the outcome is vari- able and difficult to interpret because they also contain vitamin C, polyphenols and flavonoids, which are also potential antioxidants. One study which gave additional dietary fruits and vegetables to subjects reported an increase in the resistance of LDL to oxidation(Hininger et al, 1997) while two other studies found no effect (Chopra et al, 1996; van het Hof et al, 1999). The differing results obtained may be due to different time periods on the diets, different degrees of change in the plasma carotenoids or to different study populations(Krinsky, 2001) 3.6.2 B-Carotene and protection from cancer The strongest epidemiological evidence suggesting high intake of fruits and veg- etables might give protection against lung cancer came from prospective studies tive studies and 18 out of 20 retrospective studies(Zeigler et al, 1996). Based q ia which low plasma B-carotene was associated with a higher incidence of lung cancer. Carotenoid intake was associated with reduced cancer risk in 8 prospec the results of these studies, three major intervention studies investigated the pro- tective effect of B-carotene in the prevention of lung cancer: (a)The alpha-tocopherol, beta-carotene(ATBC) Cancer Prevention study, was a randomised-controlled trial that tested the effects of daily doses of 50mg(50 IU) vitamin E(all-racemic a-tocopherol acetate), 20 mg of B-carotene, both or placebo in a population of more than 29000 male smokers for 5-8 years. No reduction in lung cancer or major coronary events was observed with any of the treatments. What was more startling was the unexpected increases in risk of death from lung cancer and ischemic heart disease with B-carotene supplementation (ATBC Cancer Prevention Study Group, 1994) (b) Increases in risk of both lung cancer and cardiovascular disease mortality were also observed in the beta-Carotene and Retinol Efficacy Trial ( CArEt). which tested the effects of combined treatment with 30mg/d B-carotene and retinyl palmitate(25 000IU/d)in 18000 men and women with a history of ciga- rette smoking or occupational exposure to asbestos(Hennekens et al, 1996)systems (Olson et al, 2000). The enzyme responsible for the conversion of retinol to HRR has not been characterised. 3.6 Health-related roles of b-carotene 3.6.1 b-Carotene as an antioxidant The ability of carotenoids to act as antioxidants can be measured in vitro, ex vivo, or in vivo. LDL isolated from an individual who has been supplemented with carotenoids and then evaluated for its antioxidant activity is an extension of an in vivo study, i.e. ex vivo. However, when carotenoids are added to plasma and then the oxidisable value of the LDL is measured it is more like an in vitro model (Krinsky, 2001). Many studies report using the ex vivo method of measuring the oxidisability of the LDL particles after feeding increased amounts of carotene￾containing foods. However, when using fruits and vegetables the outcome is vari￾able and difficult to interpret because they also contain vitamin C, polyphenols and flavonoids, which are also potential antioxidants. One study which gave additional dietary fruits and vegetables to subjects reported an increase in the resistance of LDL to oxidation (Hininger et al, 1997) while two other studies found no effect (Chopra et al, 1996; van het Hof et al, 1999). The differing results obtained may be due to different time periods on the diets, different degrees of change in the plasma carotenoids or to different study populations (Krinsky, 2001). 3.6.2 b-Carotene and protection from cancer The strongest epidemiological evidence suggesting high intake of fruits and veg￾etables might give protection against lung cancer came from prospective studies in which low plasma b-carotene was associated with a higher incidence of lung cancer. Carotenoid intake was associated with reduced cancer risk in 8 prospec￾tive studies and 18 out of 20 retrospective studies (Zeigler et al, 1996). Based on the results of these studies, three major intervention studies investigated the pro￾tective effect of b-carotene in the prevention of lung cancer: (a) The alpha-tocopherol, beta-carotene (ATBC) Cancer Prevention study, was a randomised-controlled trial that tested the effects of daily doses of 50 mg (50 IU) vitamin E (all-racemic a-tocopherol acetate), 20 mg of b-carotene, both or placebo in a population of more than 29 000 male smokers for 5–8 years. No reduction in lung cancer or major coronary events was observed with any of the treatments. What was more startling was the unexpected increases in risk of death from lung cancer and ischemic heart disease with b-carotene supplementation (ATBC Cancer Prevention Study Group, 1994). (b) Increases in risk of both lung cancer and cardiovascular disease mortality were also observed in the beta-Carotene and Retinol Efficacy Trial (CARET), which tested the effects of combined treatment with 30 mg/d b-carotene and retinyl palmitate (25 000 IU/d) in 18 000 men and women with a history of ciga￾rette smoking or occupational exposure to asbestos (Hennekens et al, 1996). 42 The nutrition handbook for food processors