MIAMI, FLORIDA. A vitamin D deficiency is widespread in northern latitudes and has been associated with an increased risk of osteoporosis and certain cancers, notably breast, colon and prostate. The main sources of vitamin D are sunlight exposure and supplementation with dietary sources playing a minor role. Since sunlight is capable of synthesizing large amounts of vitamin D, it has generally been assumed that people living in southern latitudes would be fairly immune to a vitamin D deficiency. Researchers at the University of Miami School of Medicine now dispute this assumption.
Their study included 77 men and 135 women with an average age of 55 years (18-88 years). The participants completed food frequency and sun exposure questionnaires at the end of winter (March 2000) and at the end of summer (September 2000) and had blood samples drawn and tested for 25- hydroxyvitamin D [25(OH) D], 1,25-dihydroxyvitamin D, and parathyroid hormone (PTH). Vitamin D deficiency was defined as a blood level of 25(OH)D below 20 ng/mL (50 nmol/L); this is the point at which PTH levels begin to rise.
The researchers found that 38% of men and 40% of women were deficient in vitamin D at the end of winter
and that 10% of men and 28% of women were deficient at the end of summer. Actual average
concentrations of 25(OH)D were 23.3 ng/mL (58.3 nmol/L) at end of winter and 26.8 ng/mL (67.0 nmol/L) at
end of summer. A higher intake of supplemental vitamin D (800 IU/day or more) and greater sun exposure
were associated with higher levels of 25(OH)D, but there was no association between 25(OH)D level and
age. The researchers suggest that the higher than expected prevalence of vitamin D deficiency in southern
Florida can be explained by sun avoidance and the use of sunscreens because of the heat and increased
awareness of the risk of developing skin cancer.