Vitamin D, also known as the sunshine vitamin, is a hormone that your body produces when your skin is exposed to the sun. You can also get some vitamin D from your diet, although few foods contain significant amounts of it.
Still, sun exposure and diet alone are rarely sufficient to maintain optimal vitamin D levels (
Maintaining optimal vitamin D levels is crucial for the health of your bones, brain, and immune system. Furthermore, it has been suggested that adequate vitamin D levels may help prevent unwanted weight gain (
This article reviews whether a vitamin D deficiency can cause weight gain, and if so, how to overcome it.
People with overweight and obesity appear more likely to have low vitamin D levels, compared with people with weights falling within the “normal” body mass index (BMI) range. This has caused some to suggest that low vitamin D levels may cause weight gain (
A few studies seem to support this theory. In one study, women were given 1,000 IU (25 mcg) of vitamin D or a placebo each day for 12 weeks.
By the end of the study, women in the vitamin D group lost 5.9 pounds (2.7 kg) of fat, compared with around 1.1 pounds (0.5 kg) for those in the placebo group.
The women in the vitamin D group also gained 3.1 pounds (1.4 kg) more muscle than those in the placebo group. Yet, there were no significant changes in waist circumference or total body weight (
Similarly, a recent review of 11 weight loss studies suggested that supplementing with 25,000–600,000 IU (625–15,000 mcg) of vitamin D monthly for 1–12 months may reduce BMI and waist circumference in those with overweight or obesity.
However, these changes remain very small and no significant differences in total body weight were noted (
Despite these findings, the current body of research suggests that consuming higher amounts of vitamin D has little effect on weight gain or loss. Still, more studies differentiating between body weight and body fat may be needed to properly evaluate this effect (
Why do people with overweight or obesity often have lower vitamin D levels?
Currently, most researchers believe that the lower vitamin D levels observed in people with overweight or obesity may be explained by other factors.
For instance, since vitamin D is stored in fatty tissues, people with larger amounts of body fat may need greater amounts of vitamin D to maintain blood levels similar to those of people of lower body weights (
Accordingly, experts suggest that people with overweight may need 1.5 times more vitamin D than individuals with BMIs in the “normal” range to maintain similar blood levels, whereas people with obesity may require 2–3 times more (
People with overweight or obesity often have lower vitamin D levels than people with BMIs in the “normal” range. Still, evidence to suggest that low vitamin D levels cause weight gain or make it more difficult to lose body fat is limited.
Over time, suboptimal sun exposure or low amounts of vitamin-D-rich foods in the diet may cause you to develop a vitamin D deficiency.
Signs and symptoms of vitamin D deficiency
Vitamin D deficiency isn’t typically associated with noticeable symptoms unless the deficiency is severe, so most people don’t know they’re deficient until they have a blood test. However, prolonged, severe deficiency can result in the following symptoms (
- bone pain or deformities
- muscle spasms
- dental abnormalities
- heart problems
If you recognize any of the above symptoms, make sure to discuss them with your healthcare provider to rule out a vitamin D deficiency.
People most at risk of vitamin D deficiency
Although a vitamin D deficiency can affect anyone, certain groups of people may be at a greater risk.
Older individuals, as well as those who have darker skin tones or spend little time outdoors, may likewise have an increased risk of deficiency due to a reduced ability to produce sufficient vitamin D from sun exposure alone (
Furthermore, vitamin D deficiency is more common in people with obesity (
Finally, certain prescription medications may accelerate vitamin D breakdown in the body, in turn, possibly increasing the risk of vitamin D deficiency (
Getting your blood vitamin D levels tested
If you suspect you may have low vitamin D levels, consider getting your blood levels tested to rule out a vitamin D deficiency.
Optimal blood levels tend to fall within the 30–100 ng/mL range. Values below 20 ng/mL are usually defined as a mild deficiency, and those below 10 ng/mL are considered a moderate deficiency. Vitamin D levels below 5 ng/mL are considered a severe deficiency (
A proportion of health professionals recommend that you get your blood vitamin D levels tested twice per year — once in the spring and once again in the fall.
Doing so can help you evaluate your current vitamin D levels in relation to your sun exposure and tailor your vitamin D intake or supplement regimen accordingly.
People with a vitamin D deficiency may experience a range of symptoms. If you suspect you may have low vitamin D levels or fall in one of the at-risk categories, consider getting a blood test to rule out a deficiency.
There are many ways to improve your vitamin D levels.
Your body can produce this vitamin from cholesterol when your skin is exposed to ultraviolet B (UVB) sun rays (
According to experts, exposing around 40% of your skin for at least 20 minutes to the midday sun, without wearing sunscreen, is sufficient for most people to produce enough vitamin D (
However, those with darker complexions or living more than 35 degrees above or below the equator may find it difficult to produce enough vitamin D from the sun alone. Smog levels, cloud cover, altitude, and the season are other influencing factors to consider (
Diet and supplements
The reasons described above make it important to ensure you include vitamin-D-rich or vitamin-D-fortified foods in your diet. Some examples include fatty fish, mushrooms, fortified dairy- or plant-based milks, eggs, liver, and other meats (
The reference daily intake (RDI) for vitamin D is currently set at 600 IU (15 mcg) per day for adults, and 800 IU (20 mcg) per day for people who are pregnant (16).
However, some experts argue that these recommendations are far too low to maintain optimal vitamin D levels (
Keep in mind that vitamin D is a fat-soluble vitamin, which means that taking excessive amounts over long periods may cause it to accumulate in your tissues up to levels that can be toxic.
Although vitamin D toxicity is rare, taking extremely high doses of vitamin D over prolonged periods may result in dangerous side effects. The most common cause of vitamin D toxicity is accidental overdose (
This can result in nausea, vomiting, muscle weakness, pain, poor appetite, dehydration, brain disturbances, heart and kidney problems, and in severe cases, even death (
The best way to avoid vitamin D toxicity is getting your blood vitamin D levels checked before and during supplementation, as well as working with your healthcare provider to adjust the dosage accordingly.
You can improve your vitamin D levels through a combination of sun exposure, diet, and supplementation. Regularly monitoring your blood vitamin D levels can help you tailor your supplement regimen and reduce your risk of vitamin D toxicity.
A vitamin D deficiency is unlikely to cause weight gain. However, it may cause other health problems or unpleasant symptoms, which are worth avoiding.
You can maintain adequate vitamin D levels through a combination of limited sun exposure, a vitamin-D-rich diet, and taking vitamin D supplements.
If you suspect that you have suboptimal vitamin D levels, consider getting your blood levels tested to rule out a deficiency. Regularly doing so can also help you tailor your supplement regimen and reduce your risk of vitamin D toxicity.