To assess vitamin and mineral intakes in the studied 6-year-olds, we chose an estimated food record. This method has the advantage of eliminating the problem of forgetting and improves estimation of portion size because the information is recorded at consumption [
29]. Since food record carries a higher respondent burden [
29], we chose a three-day period. Moreover, this method was most frequently used in the previous studies on vitamin and mineral intakes in children [
14],[
18],[
30]. The methods used in other studies included a four-day estimated food record [
10], a seven-day weighed food record [
13], food frequency questionnaire [
15],[
16], one 24-hour dietary recall [
11],[
12],[
19] or a combination of 24-hour dietary recall and food frequency questionnaire [
17]. The differences in vitamin and mineral intakes observed in the studied 6-year-olds and in the previously studied children [
10]-[
19] are surely caused by methodological differences. However, most probably various food habits explain most of these differences. For example, vitamin D intake was very low in all of the previously studied children [
10],[
14],[
15],[
17],[
30] irrespective of the method of dietary assessment and intake of vitamin A was much higher in Polish children, both in the studied 6-year-olds and in the previously studied 4-6-year-olds [
19], in comparison to children from other countries, which may be explained by Polish food habits.
Vitamin intakes
Mean intakes of all the analysed vitamins, except for vitamin D, were well above the reference values which implies low risk of inadequate intakes in the studied 6-year-old children. It is particularly favourable in the case of vitamins B
1, B
2, B
6, B
12 and folic acid. This is because inadequate intakes of these vitamins are linked to elevated plasma homocysteine concentration which, in turn, is related to increased risk of cardiovascular diseases, such as coronary heart disease and stroke [
31],[
32]. This is of great importance to the studied children because of their excessive intake of saturated fatty acids and animal protein along with inadequate intake of polyunsaturated fatty acids, which pose the risk of developing cardiovascular diseases, as reported in the previous article [
7]. Therefore, inadequate intakes of B vitamins would aggravate the risk of developing these diseases in the studied 6-year-olds. Additionally, the same effect would have inadequate intakes of antioxidant vitamins and so it is highly favourable that intakes of β-carotene and vitamins E and C pose low risk of inadequate intake in the studied children.
The only major concern in the studied 6-year-olds is low intake of vitamin D which implies high risk of inadequate intake. Similar or even lower intakes of vitamin D were observed in 4-10-year-old [
10] and 7-year-old [
30] British children, and in Spanish 6-9-year-old children [
17]. Also, Belgian 4–6.5-year-olds [
14] were characterised by lower intake of vitamin D compared to the studied 6-year-olds and almost all of them had intakes lower than Belgian recommendations. Such low intake of vitamin D is highly disconcerting because it may adversely affect the studied children’s bones and teeth [
33],[
34]. Moreover, studies imply that deficiency of this vitamin has negative impact on insulin resistance and β cell function [
35]-[
37] increasing the risk of diabetes. Although vitamin D is synthesised as a result of exposure to solar ultraviolet-B irradiation [
38], in Polish climatic conditions such low intake of vitamin D is unlikely to be compensated by cutaneous synthesis of this vitamin. It is highly surprising that the staff of preschools promoting health failed to spread the recommendation of eating fish frequently which would prevent inadequate vitamin D intakes in the studied children.
In the previous studies on vitamin intakes, 6-year-old children were included in groups of children of various age ranges [
10]-[
19], therefore, direct comparison to other studies is not possible. Only nutrient density may be compared directly because it is not dependent on total energy intake. In Cretan 5.7-7.6-year-old children [
18] nutrient densities were higher than in the studied 6-year-olds for six out of nine analysed vitamins, that is for vitamin B
1, B
2, B
6, folic acid, niacin and vitamin C [
18]. Serra-Majem et al. [
17] and Glynn et al. [
30] also analysed nutrient densities but in the former study the amounts of vitamins were given per 1000 kJ of energy intake while in the latter study only statistically significant differences according to gender were analysed and no values were presented.
Although vitamin intakes cannot be compared directly to other studies, it is interesting to note that intake of vitamin A in the studied 6-year-old children was much higher than in British 4-6-year-olds [
13], but also much higher than in older groups of children: 4-10-year-old [
10] and 7-year-old [
30] British children, 6-7-year-old [
15],[
16] and 6-9-year-old [
17] Spanish children, and even in the United States 6-11-year-olds [
12]. In Polish 4-6-year-olds [
19], intake of vitamin A was also lower in comparison to the studied 6-year-old children, but it was higher than in children from other countries irrespective of age. In comparison to those studies in which intakes of retinol [
10],[
13],[
19],[
30] and β-carotene [
13],[
19],[
30] were analysed, intakes of these nutrients were also the highest in the studied children as well as in the previously studied Polish 4-6-year-olds [
19]. This high intake of vitamin A in the studied 6-year-old children may be explained by high consumption of carrot juice which is very popular in Poland, especially among children and adolescents. There are many brands of carrot juice in Poland addressed particularly to the youngest consumers. Moreover, the studied children attended preschools promoting health where the staff tried to implement the habit of eating vegetables. The region where the studied children lived is not affluent and carrot which is not an expensive vegetable was often consumed by the children at preschool. The other habit which surely increased vitamin A intake is daily use of butter which is in Poland the most popular fat to spread on sandwiches.
In the previous studies, which reported vitamin intakes in children of similar age to the studied 6-year-olds, the populations of children were divided according to gender [
10],[
12]-[
14],[
17]-[
19],[
30], except for the Spanish 6-7-year-olds [
15],[
16] whose intakes were analysed according to the city where the children lived. However, statistically significant differences according to gender were tested only in two of those studies [
14],[
30].
It was expected to find many statistically significant differences in vitamin intakes between the studied girls and boys. However, it turned out not to be true in the studied children. Glynn et al. [
30] found statistically significant differences in intakes of five vitamins in English 7-year-olds, while Huybrechts and De Henauw [
14] found significant differences in intakes of four vitamins in Belgian 4–6.5-year-olds.
In the previous studies, vitamin intakes were usually reported to be higher in boys than in girls [
10],[
12]-[
14],[
17]. Only in 7-year-old English children [
30], girls were characterised by higher intake of vitamin A, retinol and β-carotene, and in 4-6-year-old Polish children [
19] girls were characterised by higher intakes of vitamin A, β-carotene, vitamin B
2, niacin and vitamin C. However, these differences were minor and statistically insignificant. Quite opposite, Huybrechts and De Henauw [
14] found statistically significantly lower intakes of vitamins D, B
1, B
2 and C in Belgian 4–6.5-year-old girls in comparison to their male peers, while Glynn et al. [
30] in the group of English 7-year-olds found statistically significantly lower intakes of vitamins B
1, B
2, B
6, niacin and folic acid in females in comparison to males.
Among the previous studies on vitamin intakes in children of similar age to the studied 6-year-olds, nutrient densities for vitamins were analysed only in three of them [
17],[
18],[
30]. Unlike in the studied 6-year-olds, nutrient densities for vitamins were not always higher in girls. Glynn et al. [
30] found higher nutrient densities in English 7-year-old girls only for vitamin A, retinol and β-carotene, however, all these differences were statistically significant. Smpokos et al. [
18] reported higher nutrient densities in Cretan 5.7-7.6-year-old girls for as many as six out of nine analysed vitamins but Serra-Majem et al. [
17] reported higher nutrient densities in 6-9-year-old Spanish girls for only three out of ten vitamins. However, neither Smpokos et al. [
18] nor Serra-Majem et al. [
17] tested statistically significant differences according to gender.
Mineral intakes
It is surprising that the studied 6-year-old children are at risk of inadequate calcium intake. The importance of drinking milk to children’s bone health has been spread throughout the Polish society for many years and even television has broadcast a series of spots promoting the habit of daily milk drinking. Also, the producers of dairy products use this recommendation in the commercials. Moreover, the children attended preschools promoting health and therefore it would seem obvious that basic nutritional guidelines should be promoted by the preschool staff. Most of the preschool staff and the studied children’s parents knew that high intake of milk and dairy products in childhood prevents osteoporosis [
39],[
40] and that milk and dairy products are rich sources of calcium [
41],[
42]. The adverse effect of inadequate calcium intake may be aggravated by the abovementioned inadequate vitamin D intake and by quite high phosphorus intake. Although the studied children did not exceed the UL, phosphorus intake was much higher than calcium intake. This may disturb the proportion of calcium to phosphorus which should be about 1.2 : 1 in children’s diet according to the Polish recommendations [
43].
Another adverse characteristic of the studied 6-year-olds’ diets was excessive intake of sodium found in all of the studied children. Exceeding sodium UL poses the risk of developing hypertension, particularly when taking into account quite low potassium intake. Although EAR for potassium has not been established, mean intake below AI shows the need to increase intake of this mineral to prevent hypertension in the studied 6-year-olds. It is unexpected that the preschool staff failed to convince the parents of the necessity to reduce salt intake and did not implement this simple rule during the preparation of preschool meals. It is even more surprising when taking into account that the majority of both the preschool staff and the studied children’s parents knew that high salt intake increases the risk of hypertension [
39],[
40]. These findings confirm the necessity to implement programme aimed at reducing salt intake as proposed in the previous article [
44].
It is also disconcerting that manganese intake exceeded UL in about a half of the studied children. However, bioavailability of this mineral from food sources have been found to be affected by other dietary factors [
23], such as phytate which reduces the efficiency of absorption of manganese [
45]. Therefore, blood manganese concentration should be measured in the studied children to conclude whether manganese intake is excessive.
Similarly to vitamin intakes, also mineral intakes cannot be compared directly to the results of other studies because of the age differences among the studied populations of children. However, it is important to note that sodium intake in the studied children was higher than in 4-6-year-old Polish children [
19] and much higher than in 4-6-year-old British children [
13] and 4–6.5-year-old Belgian children [
14]. Moreover, it was higher even than in older children: British 7-year-olds [
30], as well as 6-7-year-old [
15],[
16] and 6-9-year-old [
17] Spanish children. Nutrient densities for calcium, potassium and iron in the studied children were lower than nutrient densities for these minerals in Cretan 5.7-7.6-year-olds [
18]. However, nutrient density for sodium in the studied 6-year-olds was much higher than in Cretan 5.7-7.6-year-olds [
18]. Nutrient densities for other minerals were not analysed by Smpokos et al. [
18].
Contrary to expectations and similarly to vitamin intakes, there were statistically significant gender differences in the intakes of only two minerals in the studied 6-year-olds. Among those studies in which differences in mineral intakes were tested according to gender, only two of them reported statistically significant differences [
14],[
30].
Higher intakes of all the analysed minerals in the studied 6-year-old boys compared to their female peers, were also observed in all of the previously studied children [
10],[
11],[
13],[
14],[
17],[
19],[
30]. Only calcium intake in Polish 4-6-year-old boys [
19] and magnesium intake in 4–6.5-year-old Belgian boys [
14] were not higher than in their female peers. Moreover, Huybrechts and De Henauw [
14] and Glynn et al. [
30] reported these differences to be statistically significant, except for selenium intake in 7-year-old English boys [
30].
Higher nutrient densities for most of the analysed minerals in the studied 6-year-old girls compared to their male peers were not as noticeable as in the case of vitamins. Smpokos et al. [
18] reported higher nutrient densities for three out of four minerals in Cretan 5.7-7.6-year-old girls but Serra-Majem et al. [
17] – only for two out of six minerals in Spanish 6-9-year-old girls.