What Causes Vitamin D Deficiency
The increased melanin pigment in darker skin reduces the skin's ability to make vitamin D from sunlight. Studies show that older adults with darker skin are at particularly high risk of vitamin D deficiency.
Those who are clinically obese, with a body mass index (BMI) of over 30, frequently have low levels of vitamin D. Vitamin D in the blood is extracted by the fat cells, which alters its availability for release in the body.
The only way to know if you are receiving sufficient vitamin D on a daily basis from your diet and sunshine is by an expensive 25-hydroxy blood test which is not routinely performed. Unfortunately, you are unlikely to know if you are vitamin D deficient until it is too late and you have brittle bones, frequent fractures or osteoporosis. To be on the safe side, take a supplement of vitamin D daily. Current recommended requirements of vitamin D are 800-1000 IU, but most informed sources feel this is woefully inadequate and recommend double that amount.