Shining The Light On Obesity

Today, childhood obesity is a major global health crisis. A systematic analysis representing 188 countries revealed that worldwide prevalence of childhood overweight and obesity rose by nearly 50 percent over a span of three decades. If this trend continues, the global prevalence of childhood obesity could well reach 60 million by 2020.

The implications of this crisis are numerous and far reaching as it involves both the individual and society. Being obese in childhood has shown to be associated to increased risks for chronic conditions such as insulin resistance inflammation, hypertension and dyslipidaemia. Moreover, it can predict adult illness and compromise longevity.

To prevent this, extensive research has been conducted to investigate associations between childhood obesity and other common risk factors, one such being vitamin D deficiency. To date, vitamin D status and fat mass have been shown to be inversely correlated, and recent intervention trials indicate that correcting the poor vitamin D status associated with obesity may attenuate some of the comorbidities of obesity.

Bradley Stemke, Washington, US

Hypovitaminosis D is a significant problem among people of all ages around the world. Its estimated worldwide prevalence in children and adolescents is rather wide (29-100 percent) and surveys show it to be in part related to the degree of adiposity: healthy weight–21 percent, overweight–29 percent, obese–34 percent, and severely obese–49 percent.

Therefore, obese children are particularly vulnerable, both to being hypovitaminosis D, as well as having additional obese-related health problems.

However, it is not clear if hypovitaminosis D contributes to, or is a consequence of, obesity, or whether there are regulatory interactions between excess adiposity and vitamin D activity. It is thought though, that vitamin D enhances peripheral/hepatic uptake of glucose, attenuation of inflammation, and/or regulation of insulin synthesis/ secretion by pancreatic β-cells.

Recommendations of daily dietary allowance of vitamin D for children by medical societies or associations around the world varies from lower than 600 IU (15 μg), to 1,000 IU (25 μg). However, these are generally intended for healthy populations; the requirements for most obese youth would likely be different.

In fact, obese individuals are approximately half as efficient in using vitamin D as their lean counterparts. For every 2.5nmol/L (1 ng/mL) increase in serum 25(OH) D concentrations, an estimated 100 IU of vitamin D is required for non-obese individuals, whereas approximately 205 IU–more than double–is required for obese individuals.

Obese children were also found to require a higher dose of vitamin D, when a supplementation study found that hypovitaminosis D persisted in 24 percent of obese versus 11 percent of non-obese African-American children despite equal given dosages of 400 IU per day for four weeks.

Schlaeger Kaiserslautern Germany

Meeting vitamin D needs through the skin’s vitamin D synthesis from sunlight depends on the photo-conversion of 7-dehydrocholestrol to pre-vitamin D3 by ultraviolet B (UVB) light (wavelength =209–315 nm). Several factors such as season, latitude and time of day affect the skin’s ability to produce vitamin D3 as they alter the absorption of UVB photons by the ozone layer.

Further, with the limited sun availability throughout the year in many locations and concerns for skin cancers, relying on the sun to provide sufficient vitamin D in obese children is neither practical nor prudent.

Likewise, obtaining adequate vitamin D from natural food sources alone is generally not achievable either since only a limited number of foods naturally contain the vitamin. Foods rich in the vitamin include fish liver oils, fish, and organ meats, and to a lesser extent, egg yolks and sun-dried mushrooms.

To increase intake of the vitamin from foods, countries fortify foods such as milk, milk products or cereals. However, the consumption of milk, the most common vehicle for vitamin D fortification, generally declines with increasing age in children.

Therefore in obese children, vitamin D supplementation is warranted. Both varieties of the vitamin, D2 and D3 can be used as a food fortificant or dietary supplement, though D3 dominates.

In studying vitamin D absorption, it has been found that several fat-soluble molecules including dietary cholesterol, phytosterols, and vitamins A, E and K inhibit or compete with the vitamin. Also, health conditions characterised by fat malabsorption can increase the risk for vitamin D deficiency.

Therefore, with vitamin D deficiency being prevalent in childhood obesity and excess adiposity linked with poor vitamin D status, and further associations of this deficiency with several health implications, research findings suggest that the vitamin D needs of obese children are greater than the non-obese, and that weight loss can improve vitamin D status.