The prevalence of metabolic syndrome (MetS) has been estimated anywhere from 2% to 9.4% for US

adolescents and varies depending on the definition used (1-3). A more recent report based on the National

Health and Nutrition Examination Survey (NHANES 1999-2002) estimated the prevalence of MetS as

high as 23% for overweight/obese children aged 12-18 years (4). MetS components in childhood are

carried into adulthood (5, 6). With the growing obesity epidemic and the positive relationship between

obesity and MetS (7), research aimed at understanding the risk factors for MetS in children is needed and

is likely to have important public health implications.

Diet is a known risk factor for MetS, although contributions of individual dietary components to MetS

remain relatively ambiguous for children and adolescents. In particular, associations between dairy intake

and MetS remain unclear, although several studies, mainly in adults, suggest a protective effect crosssectionally

(8-10) and prospectively (11, 12). The Coronary Artery Risk Development in Young Adults

(CARDIA) study, a 10-year prospective study, reported a lower incidence of MetS (OR: 0.28; 0.14-0.58)

among overweight individuals consuming the highest compared with the lowest dairy category (12).

Little information exists regarding this relationship in children and adolescents. A recent cross-sectional

study observed a decreased likelihood of MetS with higher frequency of dairy, fruit, and vegetable

consumption in children aged 6-18 years living in Iran (13).

Calcium and vitamin D are two major nutrients found in dairy products that may play a protective role

against MetS (10, 14-16). Serum 25-hydroxyvitamin D is used to assess overall vitamin D status. A few

population-based studies have found inverse associations between 25(OH) D and MetS (17, 18). Data

regarding the relationship between calcium, vitamin D, and MetS are limited for children. However, a

cross-sectional study of 217 obese children aged 7-18 years found that vitamin D insufficiency was

associated with several MetS risk factors including higher BMI and systolic blood pressure and lower

HDL-cholesterol concentrations (19). Therefore, examining the potential relationship between dietary

calcium, serum vitamin D and MetS may be important in understanding the associations.

Higher circulating levels of IGF-1 have been associated with risk of certain types of cancer such as

prostate cancer (20, 21), whereas lower levels have been related to other chronic conditions such as

obesity and MetS (22, 23). In several studies, IGF-1 has been positively associated with dairy and milk

intake (24-26). Rich-Edwards et al (27) reported results from two pilot studies examining associations

between milk intake and IGF-1 as follows: 1) Mongolian children showed significant increases in IGF-1

and other factors with whole milk intake over 1 month, and 2) girls living in Boston showed small

increases in IGF-1 when consuming lowfat milk compared with a vegetable-based milk substitute over a

1 week period; these findings were not statistically significant. Rogers et al (26) found that milk and

dairy intakes were associated with IGF-1 and its binding protein (IGFBP-3) concentrations for all

children and for boys after adjustment. These associations were no longer statistically significant after

additional adjustment for protein intake, suggesting that protein may be an important mediator in this

relationship. In that study, dairy intake was positively associated with leg length in boys but not in girls,

and it appeared that IGF-1 played a role in this relationship as the association was attenuated after

adjustment. The mechanism by which IGF-1 is related to milk consumption is not fully understood.

Possible explanations include the high protein content of milk and dairy (26, 28) and/or constituents in

milk that may not be degraded/deactivated during digestion, such as growth hormones used in milk

production (27). More research is needed to identify the exact mechanism by which milk intake increases

IGF-1 and other growth factors. A recent population-based study of 6,810 British subjects found that

serum 25(OH)D and IGF-1 concentrations were inversely associated with MetS. However, associations

with IGF-1 were not statistically significant for participants with the lowest vitamin D concentrations,

indicating that both need to be considered in future research studies (22). Research projects that consider

all of the nutrients and factors discussed above are needed, especially in child and adolescent populations.