FREQUENCY OF CONSUMPTION OF PRODUCTS AND FOODS – SOURCES OF VITAMIN D AND CALCIUM – AMONG SECONDARY SCHOOL STUDENTS

Małgorzata Woźniewicz, Jan Jeszka, Karolina Sadowska, Joanna Bajerska
Department of Human Nutrition and Hygiene University of Life Sciences in Poznań, Poland

ABSTRACT

The aim of the study was to evaluate the frequency of consumption of foods, which are sources of vitamin D and calcium, among secondary school youth depending on sex, body weigh status and physical activity. The investigated population included 618 students (305 girls and 313 boys) aged 16 to 20 years, from 8 randomly selected secondary schools in the city of Poznań. Dietary intake data was obtained using a Food Frequency Questionnaire (FFQ), and physical activity was assessed with the use of the International Physical Activity Questionnaire (IPAQ). It was found that boys in comparison to girls consumed more frequently (p < 0.05) products containing higher amounts of vitamin D and calcium (hard cheese, fish, fish preserves and seafood, eggs). Also young subjects with higher level of physical activity in comparison to less active ones consumed more often (p < 0.05) products rich in vitamin D and calcium (milk, yoghurt, kefir, buttermilk, beef, veal). Overweight and obese students declared more rarely (p < 0.05) consumption of some foods rich in calcium as well as sweets in comparison with students with a proper body mass. The findings of this study show that overweight and obese, as well as physically non-active students, especially girls, may be at risk of an insufficient supply of calcium and vitamin D. Moreover, it seems that the estimation of dietary habits of overweight and obese students might be burdened with a respondent error.

Key words: vitamin D, calcium, students, FFQ.

INTRODUCTION

The life styles components having an adverse effect on health, observed commonly in Poland, include inappropriate diet [14]. This is particularly alarming in view of the health hazards concerning children and teenagers. In the period of puberty, apart from an adequate supply of energy ensuring an appropriate energy balance, a sufficient supply of nutrients is also crucial [1]. Studies conducted in recent years in Poland showed that diet, both in case of children and adults, is characterized among other things by an inadequate supply of vitamin D, which demand for girls and boys aged 16–18 years as well as individuals aged 19–30 years is defined at 5 µg/day [1,5]. Moreover, evaluation of daily food rations of Poles also showed that they are inadequate in terms of calcium supply, which recommended amount for children aged 7–9 years is 900 mg/day, while for youth it is 1300 mg/day [1,5]. This is confirmed by the results of studies on the individual food habits and nutritional status in households, conducted in the years 2000–2001 by the Institute of Food and Nutrition under the auspices of FAO [14], which showed that as much as 94.6% children consumed vitamin D at a level lower than the recommended nutritional standards and most of them did not meet them even in 50%. In turn, in the group of youth the supply of this vitamin did not exceed 38% recommended level of consumption. Taking into consideration the supply of calcium the situation is also highly disadvantageous, since it has always been insufficient and in relation to recommended nutritional standards it ranged from 56 to 87% [14]. Similar results were reported by Charzewska and Weker [2], Zielke et al. [19], as well as Reguła and Woźniewicz [13], who investigated diets of different age groups.

Results of the above studies are disconcerting due to the serious consequences connected with a diet deficient in the discussed nutrients, playing a key role in the formation and maintenance of an appropriate condition of bones and whole skeleton. Experts in public health stress the fact that osteoporosis at a mature age is first of all a consequence of insufficient mineralization of the skeleton in the first two decades of life, since the rate of growth and bone mineralization is highest in the first year of life and in the first three years of puberty [9]. New publications have been appearing with increasing frequency, confirming the incidence of osteoporotic changes in the skeleton of children and teenagers [6].

Due to the health hazards connected with the insufficient consumption of vitamin D and calcium it seemed essential to conduct studies which would make it possible to broaden the knowledge concerning the risk of deficiencies of these nutrients in food rations of teenagers. The aim of the study was to evaluate the frequency of consumption of foods, which are sources of vitamin D and calcium, among secondary school youth depending on sex, BMI index status and physical activity.

MATERIALS AND METHODS

The study was conducted in the years 2007/2008 at 8 randomly selected secondary schools in the city of Poznań. The investigated population included 618 students (305 girls and 313 boys) aged 18.2 ± 0.8 years (girls: 18.3 ± 0.8 years, boys: 18.1 ± 0.8 years).

The food frequency questionnaire (FFQ) was used for the assessment of consumption of selected products and meals which are good sources of vitamin D or calcium (whole milk, skimmed milk, cottage cheese and cream cheese, cheese and blue cheese, yoghurt, kefir, buttermilk, beef, veal, poultry, pork meat, processed meats: ham, Canadian bacon, sausages, pates, fish, fish products, seafood, eggs, margarine). Products were included in the questionnaire when they contained a minimum of 0.1 ug/100 g and 100 mg/100 g  vitamin D and calcium respectively.

Respondents participating in the survey were obliged to mark which products they consumed and at what frequency in the course of the last month, indicating one of the possible answers: A – (4 – 5 per day), B – (2 – 3 per day), C – (once a day), D – (4 – 6 per week), E – (2 – 3 per week), F – (once a week), G – (2 – 3 per month), H – (once a month), J – (rarely or never). The mean monthly frequency of consumption was determined for foodstuffs supplying vitamin D or calcium. Furthermore, products which were sources of vitamin D and calcium were put into appropriate assortment groups and the amount of food consumed per day was calculated, depending on sex, BMI, the level of physical activity, and finally compared with the recommendations presented in the food pyramid. Based on data of body weight (kg) and height (cm) collected using an anthropometer, coupled with a WPT 200 OC verified medical scale (Rad Wag), BMI (kg/m²) was established. Nutritional status for students up to 18 years of age was evaluated according to centile charts of BMI for boys and girls [9], published by the Institute of Mother and Child in Warsaw [15], and for subjects > 18, according to Ferro-Luzzi [3] (Table 1).

Table 1. Anthropometric characteristics of youth

Parameters	total n = 618	girls n = 305	boys n = 313
Age [y]	18.2 ± 0.8*	18.3 ± 0.8	18.1 ± 0.8
Height [cm]	172.7 ± 9.1	166 ± 5.7	179.4 ± 6.4
Body weight [kg]	65.7 ± 12.1	59.2 ± 9.1	72.2 ± 11.1
BMI [kg/m2]	22.0 ± 3.2	21.5 ± 3.0	22.4 ± 3.2
Underweight [%]** BMI < 18.5 [kg/m2] Centile:  < 10	11 17.8 ± 0.6	12 17.8 ± 0.6	10 17.8 ± 0.5
Proper body weight [%] BMI 18.5 – 24.9 [kg/m2] Centile:  10 - 85	70 21.3 ± 1.6	74 21.1 ± 1.4	67 21.5 ± 1.7
Overweight and obesity [%] BMI > 24.9 [kg/m2] Centile:  > 85	19 27.1 ± 2.5	14 27.5 ± 2.9	23 26.9 ± 2.2

* mean ± standard deviation; ** Interpretation of body mass index for subjects up to 18 y. according to centile charts of BMI for boys and girls [15], and for subjects > 18 according to Ferro-Luzzi [3].

The mean body weight of the whole population was 65.7 ± 12.1 kg (girls: 59.2 ± 9.1 kg boys: 72.2 ± 11.1 kg), at a height of 172.7 ± 9.1 cm (girls: 166 ± 5.7 cm boys 179.4 ± 6.4 cm).

In 12 and 10% girls and boys, respectively, BMI indicated underweight, while in almost ¾ girls and 2/3 boys BMI assumed appropriate values. Overweight and obesity was recorded in 14% girls and 23% boys.

The level of physical activity was evaluated with the International Physical Activity Questionnaire (IPAQ) [18]. Based on the data, subjects were divided into two groups characterized by adequate and inadequate physical activity, but the first group included students spending a minimum of 300 minutes a week on exercise (physical education classes and recreation activity) [18].

Comparisons between intakes of distinguished groups were conducted using a one-way ANOVA. Statistical analyses were performed using statistical software STATISTICA ™ PL 8.0 (StatSoft). A P value of less than 0.05 was considered significant.

RESULTS

It was found that among products which are sources of calcium and vitamin D respondents consumed significantly most often cheese and blue cheese (27.6 ± 1.2 /month), which contain the highest levels of calcium and vitamin D among dairy products. Boys declared a significantly higher frequency of consumption for these products (girls 23.7 ± 1.7, boys 31.4 ± 1.8/month, p < 0.05). Also whole milk was consumed significantly more often by boys as compared to girls (girls 13.1 ± 2.3, boys 26.2 ± 2.2 per month, p < 0.05).

As far as products which do not contain considerable amounts of calcium, but which are good sources of vitamin D, it was shown that all products from the meat and meats products group turned out to be significantly more often selected by boys than girls. Representatives of both sexes declared that they consumed poultry meat most frequently (girls 10.1 ± 0.8, boys 14.7 ± 1.2 per month, p < 0.05), which are poorer in vitamin D – in comparison to pork (girls 6.3 ± 0.7, boys 12.7 ±1.3 per month, p < 0.05). Offal (rich sources of vitamin D) were eaten relatively rarely, on average 9.3 ± 0.8 times a month (girls 6.1 ± 0.8, boys 12.5 ± 1.5, p < 0.05). Fish, fish products and seafood, eggs and butter were consumed in food rations much less frequently that meat products, with boys including these products into their diets significantly more frequently than girls (eggs: girls 7.3 ± 1.3, boys 13.4 ± 0.6, fish: girls 4.4 ± 0.4, boys 9.0 ± 1.3, butter: girls 39.3 ± 2.3, boys 56.6 ± 2.5, p < 0.05). Furthermore, it was found that subjects significantly more often consumed butter, in comparison to margarine. The mean consumption frequency of cakes and layer cakes amounted to 11.2 ± 1.1 times a month and it did not depend on sex. The consumption of other sweets, which included cakes, biscuits, candy, chocolate bars and chocolate, turned out to be almost three times more frequent.

Based on the collected results it may be stated that boys more frequently than girls consumed products being good sources of vitamin D. This pertains to all selected groups of products, except for sweets, cakes and layer cakes, which frequency of consumption was similar in both groups.

Among products which are not sources of vitamin D, but they are sources of calcium, a significantly more frequent consumption in the group of boys was recorded only in relation to legumes (pea, beans, broad beans) in case of boys (girls 4.7 ± 0.8, boys 8.6 ± 1.3, p < 0.05) (Table 2).

Table 2. Frequency of consumption of products which are sources of vitamin D or calcium

PRODUCTS	VIT D [ug/100g]	CALCIUM [mg/100g]	Frequency of consumption (mean + standard error of mean)
			total n = 618	girls n = 305	boys n = 318
PRODUCTS WHICH ARE SOURCES OF VITAMIN D AND CALCIUM
Whole milk 3.2%	0.03	118	19.7 ± 1.3	13.1 ± 1.3a	26.2 ± 2.2b
Reduced  fat milk	0.01	121	15.9 ± 1.1	16.0 ± 1.5	15.8 ± 1.6
Cottage cheese, cream cheese	0.18	131	18.9 ± 1.0	19.8 ± 1.4	18.0 ± 1.5
Hard cheese, soft/blue cheese	0.28	644	27.6 ± 1.2	23.7 ± 1.7a	31.4 ± 1.8b
Yoghurt, kefir, buttermilk	0.02	118	22.1 ± 1.1	23.9± 1.7	20.2 ± 1.3
Ice-cream	0.08	140	12.0 ± 1.0	11.0 ± 1.5	13.0 ± 1.2
PRODUCTS WHICH ARE SOURCES OF VITAMIN D
Beef, veal	0.42	9	8.5 ± 0.9	4.6 ± 0.7a	12.4 ± 1.5b
Poultry	0.59	12	12.4 ± 0.7	10.1 ± 0.8a	14.7 ± 1.2b
Pork	0.69	13	9.5 ± 0.8	6.3 ± 0.7a	12.7 ± 1.3b
Processed meats: ham, bacon	0.52	10	28.9 ± 1.2	21.5 ± 1.4a	36.2 ± 1.9b
Sausages, pates	0.40	40	15.8 ± 1.1	10.6 ± 1.1a	21.0 ± 1.7b
Offal	0.81	61	9.3 ± 0.8	6.1 ± 0.8a	12.5 ± 1.5b
Fish, fish products and seafood	7.94	37	6.7 ± 0.7	4.4 ± 0.4a	9.0 ± 1.3b
Eggs	1.7	47	10.3 ± 0.8	7.3 ± 1.3a	13.4 ± 0.6b
Butter	0.67	13	48.0 ± 1.7	39.3 ± 2.3a	56.6 ± 2.5b
Margarines	5.3	4	14.6 ± 1.1	12.6 ± 1.5	16.5 ± 1.6
Pasta	0.14	25	22.3 ± 0.9	14.7 ± 1.6a	27.5 ± 0.9b
Cakes and layer cakes	0.72	36	11.2 ± 1.1	10.1 ± 1.4	12.4 ±1.6
Sweets (biscuits, candy, chocolate bars, chocolate)	0.09	8	29.3 ± 1.3	30.0 ± 2.0	29.0 ± 1.8
PRODUCTS WHICH ARE SOURCES OF CALCIUM
Vegetables of Brassica family	0	212	10.1 ± 0.8	10.0 ± 1.0	10.3 ± 1.2
Greens leafy vegetables	0	177	14.7 ± 1.0	14.0 ± 1.2	15.4 ± 1.6
Legumes (pea, beans, broad beans)	0	252	6.6 ± 0.8	4.7 ± 0.8a	8.6 ± 1.3b
Nuts	0	419	9.4 ± 1.0	7.9 ± 1.2	11.0 ± 1.5

* Significantly higher frequency of consumption.

Results collected in this study were also analyzed in terms of differences in consumption between physically active and physically non-active teenagers as well as between those characterized by appropriate and inappropriate BMI (Table 3).

It was found that subjects with a higher level of physical activity, in comparison to less active ones, consumed significantly more frequently (p < 0.05) these products which are sources of vitamin D and calcium (e.g. whole milk, yoghurt, kefir, buttermilk, beef, veal, poultry, meat products, ham, bacon, sausages, pates, eggs, pasta, cakes and layer cakes, greens leafy vegetables and nuts). The significant differences in the frequency of consumption were found for whole milk (inadequate physical activity 15.4 ± 1.4/month, adequate physical activity 25.6 ± 2.4/month, p < 0.05) as well as beef and veal (inadequate physical activity 6.2 ± 0.8/month, adequate physical activity 11.7 ±1.7/month, p < 0.05). However, overweight and obese students consumed yoghurt, kefir and buttermilk rarely, in comparison to students with a proper BMI (underweight 18.9 ± 2.8, proper body weight 23.8 ± 1.4, overweight and obese 17.4 ± 1.8, p < 0.05). Paradoxically, the most marked difference pertained to the declared frequency of consumption of sweets (cakes, biscuits, candy, chocolate bars, chocolate), which turned out to be markedly lower (p < 0.05) in case of teenagers with excessive BMI in comparison to individuals with an appropriate BMI or insufficient BMI (underweight 35.4 ± 4.3, proper body weight 30.8 ± 1.7, overweight and obese 20.1 ± 2.2, p < 0.05).

Table 3. Frequency of consumption of products which are sources of vitamin D or calcium

PRODUCTS	Interpretation of BMI			Level of physical activity
	underweight n = 68	proper body weight n = 434	overweight and obese n = 116	inadequate physical activity n = 357	adequate physical activity n = 261
PRODUCTS WHICH ARE SOURCES OF VITAMIN D AND CALCIUM
Whole milk 3.2%	22.0 ± 4.7	20.4 ± 1.6	15.9 ± 2.4	15.4 ± 1.4a	25.6 ± 2.4b
Reduced fat milk	14.0±3.1	15.3 ± 1.3	19.1 ± 3.0	16.2 ± 1.4	15.4 ± 1.7
Cottage cheese, cream cheese	16.3± 2.9	20.3 ± 1.3	15.3 ± 2.1	18.2 ± 1.3	19.8 ± 1.6
Cheese, soft / blue cheese	29.7±3.9	27.8 ± 1.5	25.7 ± 2.9	27.5 ± 1.6	27.8 ± 2.0
Yoghurts, kefir, buttermilk	18.9 ±2.8ab	23.8 ± 1.4b	17.4 ± 1.8a	18.2 ± 1.2a	27.5 ± 2.0b
Ice cream	10.5±1.8	13.2 ± 1.3	8.7 ± 1.6	10.6 ± 1.1	14.0 ± 1.7
PRODUCTS WHICH ARE SOURCES OF VITAMIN D
Beef, veal	7.1±2.3	9.3 ± 1.1	6.6 ± 1.4	6.2 ± 0.8a	11.7 ± 1.7b
Poultry	12.9±2.0	12.5 ± 0.9	11.4 ± 1.3	11.1 ± 0.8a	14.2 ± 1.3b
Pork meat	9.6±2.8	9.9 ± 0.9	8.0 ± 1.4	8.3 ± 0.8	11.2 ± 1.4
Processed meats: ham, bacon	23.2±2.9	30.2 ± 1.5	27.8 ± 2.6	25.8 ± 1.5a	33.3 ± 2.0b
Sausages, pates	16.6±3.6	16.0 ± 1.3	14.7 ± 2.2	14.5 ± 1.3	17.6 ± 1.7
Offal	7.8±1.9	9.9 ± 1.1	7.9 ± 1.6	7.6 ± 0.9a	11.7 ± 1.6b
Fish, fish products, seafood	8.9±2.9	7.1 ± 0.8	4.1 ± 0.4	5.7 ± 0.6	8.2 ± 1.3
Eggs	12.0±2.5	10.4 ± 0.9	9.0 ± 1.4	8.6 ± 0.7a	12.7 ± 1.5b
Butter	43.2±4.7	50.6 ± 2.2	41.3 ± 3.6	47.5 ± 2.3	48.8 ± 2.7
Margarine	15.1±3.5	15.2 ± 1.4	12.1 ± 2.1	15.0 ± 1.5	14.1 ±1.6
Pasta	15.9±3.2	12.0 ± 1.1	9.7 ± 1.7	9.9 ±0.9a	14.9 ± 1.7b
Cakes and layer cakes	12.7±3.5	12.3 ± 1.3	6.3 ± 1.3	8.9 ± 1.1a	14.5 ± 2.0b
Sweets (cakes, biscuits, candy, chocolate bars, chocolate)	35.4±4.3b	30.8 ± 1.7b	20.1 ± 2.2a	27.7 ± 1.6	31.4 ± 2.3
PRODUCTS WHICH ARE SOURCES OF CALCIUM
Vegetables of brassica family	10.4±2.8	10.5 ± 1.0	8.7 ± 1.3	9.0 ± 0.9	11.7 ± 1.4
Greens leafy vegetables	15.6±3.5	15.1 ± 1.2	13.0 ± 1.6	13.1 ± 1.1a	17.1 ± 1.8b
Legumes (peas, beans, broad beans)	4.8 ± 1.3	7.0 ± 1.0	6.5 ± 1.6	6.1 ± 0.9	7.4 ± 1.3
Nuts	8.4 ± 2.6	8.9 ± 1.1	12.2 ± 2.7	7.5 ± 1.1a	12.2 ± 1.8b

* Significantly higher frequency of consumption.

Frequency of consumption for individual groups of products was compared with the recommendations given in the food pyramid [17] and it was analyzed depending on sex, BMI and the level of physical activity (Table 4). The products supplying vitamin D or calcium and placed, at the lowest level of the food pyramid, just over cereal products and vegetables, are nuts and legumes. The frequency of consumption declared by secondary school students for this group of products was less that one serving per day (0.5 ± 0.1/day), compared to the recommendations 1 – 3 servings. Nuts and legumes turned out to be significantly more frequently consumed by boys in comparison to girls (p < 0.05).

Table 4. The number of consumed servings per day for groups of products in comparison to recommendations presented in the food pyramid

GROUPS OF PRODUCTS	according to food pyramid (servings)	NUMBER OF SERVINGS CONSUMED A DAY (MEAN + STANDARD ERROR OF MEAN)
		Sex			Interpretation of BMI			Physical activity level
		total n=618	girls n=305	boys n=318	underweight	proper body weight	overweight and obesity	inadequate physical activity	adequate physical activity
Nuts,  legumes	1 – 3	0.5 ± 0.1	0.3 ± 0.1a*	0.7 ± 0.1b	0.4 ± 0.1	0.5 ± 0.1	0.6 ± 0.1	0.5 ± 0.1	0.1 ± 0.1
Fish, poultry, eggs	1–2	1.0 ± 0.1	0.7 ±0.04a	1.3 ± 0.1b	0.8 ± 0.2	1.0 ± 0.1	1.0 ± 0.1	1.0 ± 0.1	1.0 ± 0.1
Milk and dairy products	3 - 4	3.9 ± 0.1	3.5 ± 0.2a	4.3 ± 0.2b	3.7 ± 0.4	4.0 ± 0.2	3.4 ± 0.2	3.7 ± 0.2	4.1 ± 0.2
Red meat, meat products, fats	sparingly	4.5 ± 0.1	3.4 ± 0.2a	5.6 ± 0.2b	4.1 ± 0.4	4.7 ± 0.2	3.9 ± 0.3	3.6 ± 0.2	3.8 ± 0.2
Sweets	sparingly	1.3 ± 0.1	1.2 ± 0.1	1.3 ± 0.1	1.6 ± 0.2b	1.4 ± 0.1b	0.9 ± 0.1a	1.3 ± 0.1	1.4 ± 0.1

* Different of letter description indicate of significantly differences between groups.

The next level in the pyramid is occupied by fish, poultry and eggs. The number of servings consumed by the total group of secondary school students 1–2 servings per day (1.0 ± 0.1/day) was close to the recommended level. However, when considering the number of servings eaten by boys and girls separately, significant differences were observed and a markedly insufficient consumption of fish, poultry and eggs was found in the group of young females (girls 0.7 ± 0.04/day, boys 1.2 ± 0.1/day, p < 0.05). Declared frequency of consumption for milk and dairy products was generally consistent with the recommendation of 3 – 4 servings per day, amounting to 3.9 ± 0.1/day (girls 3.5 ± 0.2/day, boys 4.3 ± 0.2/day, p < 0.05). The group of products, which according to the recommendations presented in the food pyramid should be eaten sparingly, include first of all red meat, animal fats and sweets. The consumption of the above mentioned groups of products was exceeded both by boys and girls (meat: girls 3.4 ± 0.2, boys 5.6 ± 0.2, p < 0.05, sweets: girls 1.3 ± 0.1, boys 1.4 ± 0.1). Moreover, it was shown that underweight teenagers were characterized by a significantly more frequent consumption of sweets in comparison to teenagers with appropriate and excessive BMI (underweight: 1.6 ± 0.2, appropriate body weight: 1.4 ± 0.1, overweight and obese: 0.9 ± 0.1, p < 0.05). In turn, no statistically significant differences were found in the number of servings for individual groups of products depending on the level of physical activity (table 4).

DISCUSSION

The age of respondents corresponded to the period in individual development, which is characterized by an increased demand for energy and nutrients. Nutritional errors in that period predispose to the development of numerous diseases in the successive decades of life [11]. For example diets deficient in vitamin D and calcium, it significantly increases the risk of osteoporosis at an older age [8].

Results concerning the consumption of milk and dairy products are similar to those given in a study by Pieszko-Kleinowska et al. [12]. The authors of that study reported that among students of junior high school milk was also consumed significantly more frequently by boys in comparison to girls, while cottage cheeses were more popular among girls. Differently than in this study, they recorded hard cheeses and yoghurts in case of junior high students to be more frequently selected by girls. Taking into consideration the number of servings of all dairy products it was observed that teenagers from secondary schools in Poznań consumed these products as it is recommended in the food pyramid. Contradictory results were presented by the authors in a study [11] analyzing menus of teenagers from the Pomerania region, which indicated an insufficient amount of dairy products in their diets.

Similarly as in this study, Pieszko-Klejnowska et al. [12] stated an insufficiently frequent consumption of eggs and fish, which turned out to be particularly low in the group of girls. A disturbingly low consumption of fish was also recorded in a study by Frączek [4], in which the diets of young people from the final classes of secondary school were evaluated. The promotion of consumption of fish, processed fish products and seafood should also be focused on, due to the fact that apart from their nutritional value connected with composition of fatty acids, among all the evaluated groups of products fish are the richest source of vitamin D. Certain processed fish products, such as fish preserves, are also rich in calcium, contained in fish bones, usually consumed in this type of products.

Based on the conducted studies it was found that boys significantly more often ate the products being rich sources of vitamin D and calcium. Also when the products were presented as groups similar with presented in the food pyramid, a significantly more frequent consumption for most of the analyzed groups of products was found for boys. However, in view of the energy demand of boys and girls aged 17–18 years, a declared higher frequency of consumption for most products in case of the teenage males should be rather comforting. It needs to be stressed that despite the declared much lower frequency of consumption of a vast majority of products the frequency of consumption for sweets in the group of girls was very high. This is evidence for the existence of inadequate proportions of nutrients in food rations and unhealthy eating habits in case of female secondary school students. Also in a study by Kowalska [7], the consumption of excessive amounts of sweets by school students (irrespective of their sex). Similarly, Pieszko-Klejnowska et al. was pointed out [12] and Urbańska and Czarniecka-Skubina [16] mentioned the consumption of alarmingly excessive amounts of sweets by young people.

Taking into consideration the frequency of consumption of the above mentioned products depending on the BMI value a markedly less frequent consumption of yoghurts, kefirs and buttermilk and paradoxically also sweets was observed in the group of individuals, which BMI indicated overweight or obesity. Results concerning the frequency of consumption of sweets may suggest that overweight or obese individuals could have purposely declared a lower consumption of these products, which raises doubts concerning the reliability of the data collected from these respondents. These speculations are confirmed by the recorded much lower, although statistically non-significant, declared frequency of consumption of all (except for skimmed milk) analyzed groups of products by young people characterized by a high BMI value. Also low frequency of consumption of yoghurt and kefir in the underweight and overweight groups may be disturbing, due to the nutritive value of these products and their role in supplying vitamin D and calcium.

When analyzing the frequency of consumption for individual products being good sources of vitamin D and calcium, depending on the level of physical activity, a markedly more frequent consumption was observed for most products in case of individuals characterized by the sufficient level of physical activity. A vast majority of them are products, which should be key products in the rational balanced diet of young people (greens, poultry, beef, eggs, nuts, whole milk, yoghurt, kefir, buttermilk, pasta). Collected results may suggest that individuals with higher levels of physical activity attribute more importance to the composition of their daily food rations.

Deficiencies of vitamin D and calcium may constitute a threat to the health of young people. Due to the risk of the most serious consequences such as osteopenia and osteoporosis it is necessary to undertake actions aiming at changes in eating habits in physically non-active young people, particularly young females, and focus on actual habits of individuals with excessive body weight.

CONCLUSIONS

1. Boys, in comparison to girls, significantly more often consumed a majority of products which are sources of vitamin D or calcium.

2. Secondary school students with adequate levels of physical activity consumed more often products which are sources of vitamin D or calcium in comparison to those less active ones.

3. The diet of girls is characterized not recommended by proportions of basic groups of products due to an excessive frequency of consumption of sweets and low of fish.

4. Nutritional value of the student's diet respect supply of vitamin D and calcium in case of students, especially physically non-active young women and overweight and obese ones, has to be frequently evaluated.

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Accepted for print: 23.11.2009

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Małgorzata Woźniewicz
Department of Human Nutrition and Hygiene
University of Life Sciences in Poznań, Poland
Wojska Polskiego 31, 60-624 Poznań, Poland
phone: (61) 8487339
fax: (61) 8487332

Jan Jeszka
Department of Human Nutrition and Hygiene
University of Life Sciences in Poznań, Poland
Wojska Polskiego 31, 60-624 Poznań, Poland
email: jeszkaj@up.poznan.pl

Karolina Sadowska
Department of Human Nutrition and Hygiene
University of Life Sciences in Poznań, Poland
Wojska Polskiego 31, 60-624 Poznań, Poland
email: karolina@up.poznan.pl

Joanna Bajerska
Department of Human Nutrition and Hygiene
University of Life Sciences in Poznań, Poland
Wojska Polskiego 31, 60-624 Poznań, Poland
email: Joanna.bajerska@up.poznan.pl

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Responses to this article, comments are invited and should be submitted within three months of the publication of the article. If accepted for publication, they will be published in the chapter headed 'Discussions' and hyperlinked to the article.

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