Vitamin D Deficiency and Its Health Consequences in New Zealand

Abstract

New Zealand is located in the southwestern Pacific Ocean and has warm summers with high UV exposure and some of the highest rates of skin cancers in the world. However, recent surveys have reported higher-than-expected rates of suboptimal vitamin D status. In healthy, community-dwelling, older women, 20–30% had serum 25-hydroxyvitamin D [25(OH)D] <50 nmol/L (<20 ng/ml) in summer and 50–75% in winter. In healthy, middle-aged and older men, the rates were much lower. In a national nutrition survey, 52% of adult women and 45% of adult men had serum 25(OH)D <50 nmol/l (<20 ng/ml). Similarly high rates of low vitamin D status were seen in children. In two cross-sectional studies, we found the major determinants of 25(OH)D in older men and women were surrogates of ultraviolet B exposure (skin pigmentation, month of blood sampling, exercise levels, age, and gender) and fat mass. Both seasonal variation of 25(OH)D and fat mass have a significant impact upon the diagnosis of vitamin D sufficiency. We found that summertime 25(OH)D levels approaching 70 nmol/l (28 ng/ml) in women and 90 nmol/l (36 ng/ml) in men were required to ensure year-round 25(OH)D > 50 nmol/l (>20 ng/ml). Therefore, clinicians should consider the month of sampling when interpreting the results of 25(OH)D measurements.