Asia Pacilic J Clin Nutr (1994)3, 169-177

Determinants of serum levels of retinol, β-carotene and α-tocopherol in men and women born in Australia, Greece and Italy

Paul Ireland, Damien Jolley, Graham Giles, John Powles, Kerin O'Dea, John Hopper, Joanne Williams and Ingrid Rutishauser.

Cancer Epidemiology Centre, Anti-Cancer Council of Victoria, I Rathdowne Street, Carlton South, Victoria, 3053 Australia.

 

Serum retinol, β-carotene and α-tocopherol levels were measured in a volunteer sample of 764 Australian-, Greek- and Italian-born adult residents of Melbourne, Australia. There was no difference among the ethnic groups in mean levels of serum retinol or α-tocopherol. Mean β-carotene levels were between 11 and 22% higher for Australian-born subjects. Serum β-carotene was higher in females, retinol was higher in males. The serum levels of retinol, β-carotene and α-tocopherol were significantly positively associated with serum cholesterol. Serum triglyceride was positively associated with serum retinol and α-tocopherol but negatively associated with serum ~-β-carotene. A positive association with retinol and an inverse association with β-carotene was found for alcohol consumption. Serum α-tocopherol was positively associated with dietary vitamin E. Serum β-carotene was correlated with carotene intake among subjects who had never smoked. Serum retinol increased with age in women only. These data provide a degree of cross-cultural robustness to previous findings in regard to the determinants of serum retinol, β-carotene and α-tocopherol in healthy men and women.

Introduction

There is some epidemiological evidence of an inverse association between the level of retinol in blood and cancer risk¹. The suggested mechanism is that retinol inhibits tumour promotion through the regulation of cell growth and development². Post-hepatic conversion to retinol is one possible mechanism that might explain a reduction in cancer risk associated with β-carotene³, although the more conventional explanation involves its antioxidant properties⁴. Another dietary antioxidant that has been proposed to have a preventive role in the pathogenesis of cancer and coronary heart disease (CHD) is vitamin E⁵.

Cross-sectional surveys in Australia show that migrants from southern Europe consume large amounts of leafy green vegetables and vegetable oils; both rich sources of antioxidants⁶. It is possible that Italian- and Greek-born Australians obtain some protection against CHD and cancer from dietary antioxidants because their mortality advantage is 1000 not explicable in terms of established risk factors such as serum cholesterol, cigarette smoking, obesity or physical inactivity^7,8.

It is well recognized that positive associations exist between the dietary intake of β-carotene and α-tocopherol and their levels in serum or plasma⁹. No such relationship is evident for retinol, although elevated serum retinol levels have been reported among individuals taking daily vitamin A supplements^10,11. In recent years attention has focussed on identifying other factors associated with the serum levels of retinol, β-carotene and α-tocopherol. The list includes: serum cholesterol and triglycerides, age, gender, smoking status, alcohol consumption, energy intake, relative body weight, use of antihypertensive medication, and season of the year in which the blood was taken. Establishing the relative importance of the various endogenous and exogenous determinants of the level of a nutrient in serum can best be done by performing multivariate analysis with all of the independent variables included in one regression model. In addition, the extent to which the determinants are cross-culturally robust is likely to be of biological relevance yet this has not been adequately addressed. Serum levels of retinol, β-carotene and α-tocopherol were therefore measured in a field study conducted in Melbourne, the Australian city with the largest Italian and Greek communities¹². The aims of the study were threefold: to establish whether there were differences in the serum levels of these nutrients on the basis of ethnicity; to describe a normal reference range for these nutrients in healthy Australian men and women, and to identify their determinants within a heterogeneous population using multiple linear regression.

Materials and methods

Study population and recruitment

The study population (Table 1) consisted of a volunteer sample of 764 healthy men and women who took part in the feasibility trial of the Melbourne Collaborative Cohort Study¹³. The sampling strategy was to obtain people who were likely to volunteer to be in a long-term study of their health.

 

Table 1. Characteristics of the study population, n (%).

1000

	Males			Females
	Australiana	Italiana	Greeka	Australiana	Italiana	Greeka
Age(years)
40-49	43(46.7)	13 (12.6)	39 (33.1)	62 (41.6)	14 (10.5)	66 (50.0)
50-59	24(26.1)	26 (25.2)	47 (39.8)	61 (40.9)	56 (42.1)	48 (36.4)
60-69	25(27.2)	64 (62.1)	32 (27.1)	26 (17.4)	63 (47.4)	18 (13.6)
Smoking status
Never smoker	43(46.7)	32 (31.1)	30 (28.8)	104 (69.8)	108 (81.2)	99 (75.0)
Former smoker	39(42.4)	49 (47.6)	54 (45.8)	39 (26.2)	18 (13.5)	14 (10.6)
Current smoker	10(10.9)	22 (21.4)	34 (25.4)	6 (4.0)	7 (5.3)	19 (14.4)
Body mass index (kg/m2)
<20	3 (3.3)	1(1.0)	0 (0.0)	4 (2.7)	0 (0.0)	0 (0.0)
20-24.9	26 (28.3)	9 (8.7)	23 (19.5)	70 (47.0)	21 (15.8)	28 (21.2)
25-30	56 (60.9)	74 (71.8)	75 (63.6)	57 (38.3)	62 (46.6)	81 (61.4)
>30	7 (7.6)	19(18.4)	20 (16.9)	18 (12.1)	50 (37.6)	23 (17.4)
Use vitamin supplement at least once/ week
Multivitamin	18 (19.6)	5 (4.9)	5 (4.2)	21 (14.1)	7 (5.3)	5 (3.8)
Vitamin A	1 (1.1)	1 (1.0)	3 (2.5)	2 (1.3)	2 (1.5)	2 (1.5)
Vitamin E	2 (2.2)	4 (3.9)	1 (0.8)	10 (6.7)	4 (3.0)	2 (1.5)

a Refers to country of birth, most of the Italian and Greek-born participants are Australian citizens.

 

Participation was restricted to people living within the Melbourne Statistical Division aged between 40 and 69 years who were born in Australia or who entered Australia on a Italian or Greek passport, including some who were born in Egypt or Cyprus.

Assistance was generously provided by est 1000 ablished networks within the Italian and Greek communities. Talks were give to church groups, regional clubs and people attending migrant resource centres. Articles were written in the ethnic, suburban and regular newspapers. Interviews were broadcast on ethnic and commercial radio programmes and awareness was spread further by word of mouth.

Recruitment of the different ethnic groups was staggered: the Greek-born subjects were recruited between November 1987 and April 1988, the Italian-born were recruited between May 1988 and July 1988 whereas the Australian-born were recruited between September 1988 and November 1988. Most of the Australian-born subjects had responded to an advertisement in a major metropolitan daily newspaper. Others responded to invitation letters which were distributed to several hundred households across Melbourne.

Study design and data collection

Upon enrolment, subjects were sent a self-administered questionnaire in their preferred language. Once this was returned every subject was visited in their home by a bilingual member of staff. As well as providing an opportunity to clarify or enter missing questionnaire responses as required, the purpose of the visit was to deliver a set of weighing scales and explain and demonstrate the procedure for recording weighed food intake. Records of weighed food intake were kept on two occasions, each of 4 days duration, at least 6 weeks apart. Subjects were asked to return the completed records by mail in pre-paid reply envelopes. The nutrient database comprised McCance and Widdowson's The Composition of Foods¹⁴ supplemented with certain local foods¹⁵. The composition of some Greek composite dishes was obtained from Professor A. Trichopoulou, the author of the Greek Food Composition Table¹⁶ and these were added together with some items created from recipes provided by the Italian and Greek subjects. The questionnaires, printed instructions and booklets for recording weighed food intake were also provided in Greek and Italian. The research instruments had earlier been pilot-tested on 40 Greek and Italian migrants.

The final data collection involved taking a 15-ml fasting blood sample and physical measurements such as blood pressure, weight, height, sitting height, body impedence, and waist and hip circumferences. Subjects were invited to attend one of 32 sessions held at ten different locations throughout Melbourne between March and April 1989. Data concerning age, country of birth, use of cigarettes, vitamin supplements and antihypertensive medication were obtained from the diet records. Body mass index (BMI, weight/height²) was calculated from measurements of height (metres) and weight (kilograms) taken in light indoor clothing without shoes.

The study protocol was approved by the Ethics Committee of the Anti-Cancer Council of Victoria. All subjects gave their voluntary written consent before participation.

Laboratory analyses

Blood samples were obtained from fasting subjects between 7.00 and 11.00 am. From each sample, 10 ml was collected into a pre-labelled plain tube that was immediately wrapped and covered with aluminium foil. Blood samples were kept in the dark and allowed to clot at room temperature before being transferred on ice to the laboratory within 3-4 h of phlebotomy. The samples were centrifuged and the serum removed and stored at -80°C for up to 3 months.

Serum retinol, β-carotene and α-tocopherol were measured by a commercial laboratory using reverse-phase high-performance liquid chromatography. Serum total cholesterol and triglyceride concentrations were determined using enzymatic colorimetric reagents on a Roche Cobas Fara autoanalyser by the Biochemistry Department of the Alfred Hospital, Melbourne.

 

Table 2. Descriptive statistics of serum lipids and antioxidants.

1000

			Mean	S.D.	Min	25th	Median	75th	Max
Cholesterol  (mmol/l)	Males	Italy	6.33	1.06	4.0	5.6	6.3	7.1	8.5
		Greece	6.23	1.09	3.2	5.5	6.2	7.0	9.1
		Australia	6.21	0.97	3.7	5.4	6.4	6.8	8.5
	Females	Italy	6.61	1.11	4.2	6.0	6.5	7.2	9.7
		Greece	6.26	1.03	4.3	5.5	6.3	6.9	8.9
		Australia	6.32	1.12	4.2	5.5	6.3	6.9	9.6
Triglycerides(mmol/l)	Males	Italy	2.68	3.66	0.6	1.4	1.9	2.8	33.4
		Greece	1.77	1.14	0.2	1.0	1.5	2.2	7.0
		Australia	1.70	1.04	0.4	1.0	1.4	2.1	5.1
	Females	Italy	1.84	1.03	0.5	1.1	1.5	2.3	6.1
		Greece	1.39	0.75	0.4	0.8	1.2	1.7	4.0
		Australia	1.27	0.70	0.4	0.8	1.0	1.5	4.9
Retinol (μmol/l)	Males	Italy	2.99	0.88	1.2	2.5	2.9	3.4	6.8
		Greece	2.97	0.97	0.9	2.4	2.8	3.4	6.1
		Australia	3.06	0.86	0.9	2.5	3.1	3.5	6.8
	Females	Italy	2.71	0.78	0.9	2.2	2.7	3.1	6.4
		Greece	2.53	0.94	0.9	1.8	2.4	3.1	5.3
		Australia	2.68	0.86	0.8	2.1	2.6	3.1	6.0
β-carotene (μmol/l)	Males	Italy	0.79	0.59	0.1	0.4