People who are overweight and obese appear more likely to have low vitamin D levels compared with people whose body mass index (BMI) falls within the normal range. This has caused some to suggest that low vitamin D levels may cause weight gain — but what does the research actually say?
Why Do People with Overweight or Obesity Often Have Lower Vitamin D Levels?
Most researchers believe the lower vitamin D levels observed in people with overweight or obesity may be explained by several factors. 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 with lower body weights.
People with overweight or obesity may also spend less time outdoors or eat less vitamin D-rich food. Experts suggest that people who are overweight may need 1.5 times more vitamin D than individuals with normal BMIs, while people with obesity may require 2–3 times more to maintain similar blood levels.
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 bone pain or deformities, rickets, seizures, muscle spasms, dental abnormalities, and heart problems. If you recognize any of these symptoms, discuss them with your healthcare provider to rule out a vitamin D deficiency.
Who Is Most at Risk of Vitamin D Deficiency?
Post-bariatric surgery patients: Those who have had gastric bypass surgery may have a reduced ability to absorb vitamin D from their diet.
People with digestive conditions: celiac disease, short bowel syndrome, inflammatory bowel disease, cystic fibrosis, or chronic pancreatic insufficiency all increase deficiency risk.
Older individuals: The body’s ability to produce vitamin D from sunlight decreases significantly with age.
People with darker skin tones: Melanin reduces the skin’s capacity to produce vitamin D from sunlight.
People who spend little time outdoors: Limited sun exposure is one of the most common causes of deficiency.
People with obesity: Vitamin D deficiency is significantly more common in people with obesity.
Getting Your Blood Vitamin D Levels Tested
If you suspect you may have low vitamin D levels, consider getting a blood test. Optimal blood levels fall within the 30–100 ng/mL range. Values below 20 ng/mL are usually defined as a mild deficiency, those below 10 ng/mL are considered a moderate deficiency, and levels below 5 ng/mL are a severe deficiency.
Many health professionals recommend getting your blood vitamin D levels tested twice per year — once in spring and once in autumn — to evaluate your levels in relation to seasonal sun exposure and tailor your supplementation accordingly.
Ways to Improve Vitamin D Levels
Sun Exposure: Exposing around 40% of your skin for at least 20 minutes to midday sun without sunscreen is sufficient for most people to produce enough vitamin D. However, those with darker complexions or living far from the equator may find it difficult to produce enough from sunlight alone.
Diet: Include vitamin D-rich foods such as fatty fish, mushrooms, fortified dairy or plant-based milks, eggs, liver, and other meats. The recommended daily intake is 600 IU (15 mcg) per day for adults and 800 IU (20 mcg) for pregnant women.
Supplements: If you’re unable to maintain adequate vitamin D levels through sunshine and diet alone, a supplement providing 800–4,000 IU per day may be needed. Always take vitamin D supplements with a meal containing fat for better absorption, and monitor blood levels regularly to avoid toxicity.
A Word of Caution on Vitamin D Toxicity
Vitamin D is a fat-soluble vitamin, which means taking excessive amounts over long periods may cause it to accumulate to toxic levels. Symptoms of toxicity include nausea, vomiting, muscle weakness, poor appetite, dehydration, and in severe cases, heart and kidney problems. Always work with your healthcare provider to find the right dosage for your individual needs.
Conclusion
You can improve your vitamin D levels through a combination of sun exposure, a balanced diet, and appropriate supplementation. Regularly monitoring your blood vitamin D levels helps you tailor your supplement regimen and reduce the risk of deficiency or toxicity. If you fall into any of the at-risk categories, speak with your healthcare provider about getting tested today.
— Dr. Sanjay Agrawal
Leading Pharmaceutical Consultant and Editor-in-Chief of IJMToday
