Na and salt intake
Most of the popular snacks that are very attractive to children contain a large amount of salt. In children, the daily recommended Na intake increases with age. For children younger than one year, the daily recommended salt intake is < 1 g/d (range 0.4−1.3 g/d); newborns and infants need more salt per kg of body weight than older children, in whom the adverse effects from excessive salt consumption are similar to adults. In children aged 1 to 5 and 5 to 10 years, the recommended daily intake is 2 g/d and 4 g/d, respectively; however, the actual salt intake reaches 4.9 g/d and 8.1, respectively. For those aged 10 to 20 years the recommendation is 5 g/d, although actual daily intake ranges from 6.7 to 11.0 g/d [
18].
He and MacGregor (2006) [
19] published a meta-analysis of randomized clinical trials that investigated the effect of reducing salt intake on blood pressure in children and infants. They showed that a reduced salt consumption (median reduction of 42 % in children and 54 % in infants) led to a significant decrease in blood pressure values:–1.17 mmHg (95 % CI–1.8,–0.56 mmHg) systolic and–1.29 mmHg (95 % CI–1.9,–0.65 mmHg) diastolic in children and–2.47 mmHg (95 % CI–4.0,–0.94 mmHg) systolic in infants. More recent studies confirmed those findings [
20‐
22]. Finally, a study carried out in low-income children aged 3–4 years found a higher risk of elevated systolic blood pressure in those who consumed >1200 mg of sodium/day (3.32, 95 % CI 0.98, 11.2) or had >0.5 waist-to-height ratio (8.81, 95 % CI 2.1, 36.3) [
23]. However, in other studies, no association was found between excessive consumption of sodium (i.e., exceeding recommended levels) and future high blood pressure [
24,
25].
Fatty acids, nuts, and olive oil
Fatty acids and fats are an important source of energy, and fat makes food more attractive and tasty, especially for children; however, many studies have shown the positive association between fat consumption and obesity [
26,
27]. In clinical and observational studies in children, higher consumption of total, unsaturated and saturated fats, and myristic fatty acids was associated with increased total cholesterol [
28,
29]. Thorsdottir and Ramel (2003) found that total and saturated fat consumption was associated with incidence of diabetes [
30]. Another randomized trial showed that milk low in saturated fatty acids and enriched in omega-3 polyunsaturated fatty acid (PUFA) and oleic acid reduces indices of endothelial cell activation in children aged 8–14 years [
31]. In infants, intake of total fat and monounsaturated fats correlated with apolipoprotein A1 (Apo-A1), the main apolipoprotein of HDL-cholesterol, which is responsible for the efflux of cholesterol from the body (rho = 0.18,
p = 0.036 and rho = 0.17,
p = 0.048, respectively) [
32]. The intake of polyunsaturated fatty acids was inversely correlated with apolipoprotein B (Apo-B), the main apolipoprotein of LDL-cholesterol and a marker of cardiovascular disease (rho = −0.17,
p = 0.046).
Few studies have investigated the association of cardiovascular risk factors in children with consumption of food items and food groups rich in lipids. Haro-Mora et al. (2011) showed that children consuming only olive oil, among all vegetable oils used in the study, had lower risk of increased body mass index (BMI) Z-scores (OR 0.19 95 % CI 0.04, 0.52), compared with children consuming a combination of other oils [
33]. High nut consumption (>1/4 oz. per day) in children 12–18 years old was associated with lower prevalence of overweight and obesity and lower levels of diastolic blood pressure [
34]. A 40 % lower risk of overweight (95 % CI 0.43, 0.85) was observed in the top tertile of nuts consumption among healthy children and adolescents attending Seventh Day Adventist schools, where a high proportion of students are vegetarians or vegans in accordance with religious beliefs [
35]. Among food groups with lipid-rich content, vegetable oils were associated with low fasting glucose (
β = −3.34, 95 % CI–4.1,–0.27) and added fats (cream, butter, lard, creamy dressing, and sauces) were positively associated with higher levels of triglycerides (
β =2.70, 95 % CI 0.29, 23.3) [
36].
Dairy
Recently, more attention has been paid to the association between dairy products and cardiovascular risk factors in children. Bigornia et al. (2014) showed that 10-year-olds with higher consumption of full-fat and reduced-fat dairy products had 43 % (95 % CI 0.34, 0.94) and 26 % (95 % CI 0.43, 1.3) lower probability of being overweight or having excessive body fat in 3 years, respectively. [
37]. Similar results were found in adolescents [
38]. In Mexican children, consumption of flavored milk was associated with decreased risk of obesity (O
R = 0.88,
p = 0.004); a similar association was observed for whole milk, but only in univariate analysis, and there was no association for skimmed milk [
39]. Flavored milks usually have higher energy per unit than non-flavored milk; however, the sugar and fat content of flavored milks differs according to the brand. Interestingly, consumption of skimmed milk was associated with increased adiposity in 2-to 4-year-olds, compared to consumption of full-fat milk (OR 1.64 and 1.63,
p < 0.001 for 2-year-olds and 4-year-olds, respectively) [
40].
Only a few studies have observed a positive association between consumption of milk and dairy products and adiposity in children [
41,
42]; the remainder found inverse or no associations in children and adolescents [
43]. Most of the studies about milk consumption were done in European populations; however, Lin Lin et al. (2012) found no association between milk or dairy consumption and both general and abdominal obesity surrogates in a Chinese sample of adolescents aged 11–13 years [
44]. The researchers explain this difference in outcome, compared to the European population, as a possible confounding by socioeconomic position in European countries.
Although abdominal obesity is also a cardiovascular risk factor, few studies have investigated the association of dairy products consumption with this type of obesity. In a study by Abreu et al. (2012), high milk consumption was associated with lower abdominal obesity, independently of physical activity level: even the participants with low levels of physical activity and high milk consumption had lower odds of abdominal obesity (OR 0.412, 95 % CI 0.20, 0.85), compared to highly active adolescents with low milk consumption (OR 0.928, 95 % CI, 0.56, 1.53) [
45].
Other metabolic syndrome factors, such as insulin resistance, increased blood glucose levels, and diabetes mellitus 2, have also been inversely associated with dairy consumption [
46]. In a study with school children from low-income households in Buenos Aires, higher milk consumption was associated with higher levels of the insulin sensitivity marker, homeostatic model assessment (HOMA-IR), independently of other healthy-diet factors (
β = −0.28,
p = 0.026) [
47]. However, one study of 8-year-old children compared the effect of milk and meat consumption on insulin resistance, and found a positive association between milk (but not meat) consumption and insulin concentration (103 %), insulin resistance (75 %), and C-reactive protein (26 %) [
48]. Additionally, in 10- to 16-year-olds from 11 European countries, milk consumption was correlated with incidence of diabetes (
r = 0.829;
p = 0.042) [
30]. The fat percentage of the milk might also matter; there is a hypothesis that the widespread increase in consumption of low-fat milk and decreased whole milk consumption could be related to an increased inflammation status [
49].
Regarding blood pressure, three cohort studies–two in children and one in adolescents–showed an inverse association of dairy consumption with increased blood pressure [
43,
50]. Yuan et al. (2013) showed that ≥2 servings per day of dairy products were associated with 1.74 mmHg (
p < 0.005) and 0.87 mmHg (
p = 0.010) lower systolic and diastolic blood pressure, respectively, in a fully-adjusted model. In their study, daily servings were defined according to the dairy product: milk, 250 ml; yogurt, 175 g; and cheese, 50 g. They excluded other dairy products, such as ice cream, cream, milkshakes, and combination dishes [
50]. However, in school-aged children in Mexico, high intake of high-fat dairy (i.e., produced from whole milk) was associated with higher diastolic blood pressure (
β = 8.76, 95 % CI 0.75, 2.5) and also with a higher level of HDL-cholesterol (
β = 10.37, 95 % CI 0.21, 2.0) [
36].