Vitamin D is a fat-soluble vitamin that you can get from vitamin D-rich foods or supplements. Your body is also able to make it through sun exposure.
Vitamin D is essential for maintaining strong bones and teeth, keeping your immune system healthy and facilitating the absorption of calcium and phosphorus.
Because vitamin D is not found naturally in very many foods, most health professionals recommend getting at least 5–30 minutes of sun exposure daily or taking a supplement to meet the recommended daily amount of 600 IU (15 mcg).
However, those living too far from the equator may not be able to meet their requirements through sun exposure alone. At certain latitudes, very little vitamin D can be produced by the skin for up to six months of the year.
Unfortunately, vitamin D deficiency affects nearly 50% of people worldwide.
Those at risk of deficiency include :
Obesity is another risk factor for deficiency. Interestingly, some evidence suggests that getting enough vitamin D could help with weight loss.
Studies show that a higher body mass index and body fat percentage are associated with lower blood levels of vitamin D.
Several different theories speculate about the relationship between low vitamin D levels and obesity.
Some claim that obese people tend to consume fewer vitamin D-rich foods, thus explaining the association.
Others point to behavioral differences, noting that obese individuals tend to expose less skin and may not be absorbing as much vitamin D from the sun.
Furthermore, certain enzymes are needed to convert vitamin D into its active form, and levels of these enzymes may differ between obese and non-obese individuals.
However, a 2012 study noted that once vitamin D levels in obese individuals are adjusted for body size, there’s no difference between levels in obese and non-obese individuals.
This indicates that your vitamin D needs depend on body size, meaning obese individuals need more than normal-weight people to reach the same blood levels. This could help explain why obese people are more likely to be deficient.
Interestingly, losing weight can also affect your vitamin D levels.
In theory, a reduction in body size would mean a decrease in your vitamin D requirement. However, since the amount of it in your body remains the same when you lose weight, your levels would actually increase.
And the degree of weight loss may affect the extent to which its levels increase.
One study found that even small amounts of weight loss led to a modest increase in blood levels of vitamin D.
Furthermore, participants who lost at least 15% of their body weight experienced increases that were nearly three times greater than those seen in participants who lost 5–10% of their body weight.
Moreover, some evidence shows that increasing vitamin D in the blood can reduce body fat and boost weight loss.
Some evidence suggests that getting enough vitamin D could enhance weight loss and decrease body fat.
At least 20 ng/mL (50 nmol/L) is considered to be an adequate blood level to promote strong bones and overall health.
One study looked at 218 overweight and obese women over a one-year period. All were put on a calorie-restricted diet and exercise routine. Half of the women received a vitamin D supplement, while the other half received a placebo.
At the end of the study, researchers found that women who fulfilled their vitamin D requirements experienced more weight loss, losing an average of 7 pounds (3.2 kg) more than the women who did not have adequate blood levels.
Another study provided overweight and obese women with vitamin D supplements for 12 weeks. At the end of the study, the women didn’t experience any weight loss, but they did find that increasing levels of vitamin D decreased body fat.
Vitamin D could also be associated with a decrease in weight gain.
A study in over 4,600 elderly women found that higher levels of vitamin D were linked to less weight gain between visits during the span of the 4.5-year study.
Based on these studies, it seems that the weight-related benefits of vitamin D come from increasing its blood levels, rather than supplementation itself.
Several theories attempt to explain vitamin D’s effects on weight loss.
Studies show that vitamin D could potentially stop the formation of new fat cells in the body.
It could also prevent the storage of fat cells, effectively reducing fat accumulation.
Additionally, vitamin D can increase levels of serotonin, a neurotransmitter that affects everything from mood to sleep regulation.
Serotonin may play a role in controlling your appetite and can increase satiety, reduce body weight and decrease calorie intake.
Finally, higher levels of vitamin D may be associated with higher levels of testosterone, which could trigger weight loss.
A 2011 study gave 165 men either vitamin D supplements or a placebo for one year. It found that those receiving the supplements experienced greater increases in testosterone levels than the control group.
Several studies have shown that higher levels of testosterone can reduce body fat and help sustain long-term weight loss.
It does this by boosting your metabolism, causing your body to burn more calories after eating. It could also block the formation of new fat cells in the body.
It’s recommended that adults 19–70 years old get at least 600 IU (15 mcg) of vitamin D per day.
However, supplementing with vitamin D may not be a “one size fits all” approach, as some research indicates that the dosage should be based on body weight.
One study adjusted vitamin D levels for body size and calculated that 32–36 IU per pound (70–80 IU/kg) is needed to maintain adequate levels.
Depending on your body weight, this amount may be significantly higher than the established upper limit of 4,000 IU per day.
On the other hand, doses of up to 10,000 IU per day have been reported with no adverse effects.
Still, vitamin D supplements can cause ctoxicity when consumed in large amounts. It’s best to consult your doctor before exceeding the upper limit of 4,000 IU per day.