Reduced Kidney Function and Obesity
Sometimes you get enough vitamin D from everywhere — you consume enough in your diet, get enough sunlight exposure, use supplements to keep your vitamin levels optimal — but still suffer from vitamin D deficiency. This is a peculiar situation that affects some people. It often happens because your body is unable to metabolize the vitamin D you take in.
Your kidney helps you convert the vitamin D in your body into its active form. If something happens to interfere with this process, you may become deficient in vitamin D. Kidney disease is a common cause of this condition.
Reduced kidney function may also be caused by aging. As you grow older, your kidneys naturally become less efficient. This can cause deficiency to set in. According to Cleveland Clinic [2], being over the age of 50 increases your risk of deficiency.
Being overweight can also increase your risk of vitamin D deficiency. Fat cells can remove vitamin D from the blood and prevent it from circulating properly. It is estimated [3] that people whose body mass index exceeds 30, usually have lower amounts of vitamin D in their blood.
A review of 23 studies found that obese subjects had 35 and 24 percent higher rates [4] of vitamin D deficiency compared to normal-weight and overweight subjects respectively.