At the Spring Festival stall, Jia Ling's "Hot and Hot" hit the hearts of many people, the movie was inspirational, and there was really a frenzy of weight loss in society. As we all know, obesity carries many risks, including type 2 diabetes, metabolic syndrome, cardiovascular and cerebrovascular diseases, and increased cancer risk and mortality. However, in this surging "wave of weight loss", there is one indicator that is also worth paying attention to, and that is vitamin D nutritional status.
01
Obesity predisposes to vitamin D deficiency
Vitamin D is an essential vitamin, and in addition to its direct effects on skeletal muscles, its effects outside the bones are equally important, including immune, anti-inflammatory, anti-tumor, antioxidant and other effects. Epidemiological studies have shown that obese people themselves have an increased need for vitamin D, but they are relatively underutilized, coupled with insufficient exercise and outdoor light, air pollution and conservative dress, are more likely to develop vitamin D deficiency.
25OHD is the body's "reserve pool" of vitamin D, and studies have confirmed that the serum 25OHD in obese people is about 20% lower than that in normal weight people, and the prevalence of vitamin D deficiency is higher in obese people. It has been calculated that every 1 unit increase in BMI is associated with a 1.15% decrease in the 25OHD level.
The reasons may be related to the increase of blood lipids in obesity, the inhibition of liver Cyp2r1 expression by insulin resistance, and the impaired hydroxylation of liver 25. By supplementing vitamin D preparations, the body fat and fat distribution of obese patients can be improved, and insulin sensitivity can be increased, which plays an important role in preventing the occurrence and development of obesity.
02
Vitamin D deficiency may be the cause of obesity
In fact, low vitamin D status itself can lead to the development of overweight/obesity. The satiety hormone "leptin" secreted by fat cells is positively correlated with body fat mass and inhibits adipogenesis and stimulates lipolysis by interacting with vitamin D receptors (VDRs), while vitamin D deficiency may increase appetite and lead to obesity by directly regulating leptin expression.
Several cross-sectional studies have shown that VD deficiency is associated with hyperglycemia, hyperinsulinemia, impaired β cell function, and insulin resistance. Similarly, chronic low-grade inflammation may play a key role in the development of metabolic syndrome, and the active form of vitamin D1,25(OH)2D has an anti-inflammatory effect and can also inhibit adipogenesis through receptor modulation, which sideways confirm the role of vitamin D deficiency in the development of obesity.
Due to VD deficiency, parathyroid hormone (PTH) levels increase, promoting adipogenesis through greater calcium influx in adipocytes, and decreased VD levels enhance preadipocyte differentiation into adipocytes. A recent study of large mother-infant cohorts has shown that there is also an association between maternal serum 25OHD levels and various parameters of childhood obesity characteristics.
Similarly, meta-analyses have demonstrated improvements in BMI and waist circumference, cholesterol and glucose tolerance with VD supplementation, as well as a reduction in cardiovascular risk factors. However, due to the small number of studies and significant methodological heterogeneity, the current evidence is insufficient to draw firm conclusions.
03
Weight loss and vitamin D deficiency
Although it is not unfounded to boast of the weight loss efficacy of lifestyle interventions, in fact, many obese individuals, particularly those with severe obesity and comorbidities, recommend surgery. The evidence in favour of bariatric surgery is not only due to the reduction of fat bodies, but also to the more significant benefit. However, bariatric surgery is not without the risk of complications, and there is substantial evidence that bariatric surgery is associated with a risk of vitamin D deficiency and secondary hyperparathyroidism.
In particular, the most commonly used RYGB (Roux-en-Y gastric bypass) procedure is associated with a higher risk of postoperative malabsorption and vitamin D deficiency due to duodenal and proximal jejunal bypass. Serum 25OHD levels often struggle to rise after a large increase in vitamin D intake.
Another recently promoted structured very low energy diet (VLED) for weight loss also had similar adverse effects, and studies showed no difference in the risk of vitamin D deficiency and secondary hyperparathyroidism between patients who underwent surgery and those who received VLED at two years of follow-up.
04
How to make up for vitamin D deficiency?
Although reasonable exposure to sunlight is still the best, cheapest, and safest way to obtain vitamin D, it can provide more than 90% of the body's source of vitamin D, especially in the UVB range of 290-315nm. But it is more logical that food fortification programs address the global epidemic of vitamin D deficiency.
Foods rich in vitamin D include cod liver oil, fatty fish, egg yolks, and mushrooms, however, as it is difficult to determine the proportion of vitamin D supplementation that each country stimulates from diet or through UV exposure, it may be more appropriate to develop different vitamin D supplementation strategies for different countries.
With regard to vitamin D supplementation, it is generally accepted that higher doses (2-3 times more) are required in obese patients, and according to the guidelines, vitamin D deficient patients should be supplemented with 50,000 IU per week for 8 weeks, or 6,000 IU/day of vitamin D2 or D3 to achieve serum 25 OHD >30 ng/ml, followed by maintenance therapy of 1,500 to 2,000 IU/day.
At present, more and more attention has been paid to the research of vitamin D deficiency in obese people, but there is no clear evidence that vitamin D supplementation can improve obesity metabolic outcomes. Changes in vitamin D levels need to be closely watched before and after weight loss, and in obese people with deficiency, a higher than normal weight loading dose is often required to achieve the same serum vitamin D level, but because metabolic clearance is not affected by obesity, the maintenance dose should be similar to that of the normal population.
Spring is blooming, let's soak up the sun and lose weight together in a healthy way!