According to a new national nutrition survey 40% of Irish adults have blood vitamin D concentrations that are inadequate for bone health throughout the year with a much higher prevalence during winter.
In the survey, seasonal serum 25-hydroxyvitamin D concentrations and vitamin D supplement use were analyzed in 1,132 adults (1). The results showed significant year-round prevalence rates for inadequate serum 25(OH)D concentrations: 6.7% of the participants had vitamin D deficiency (below 30 nmol/l) while 40.1% had insufficient vitamin D levels (below 50 nmol/l). The rate was higher in winter with 11.1% and 55%, respectively. Of those deficient and insufficient, 75.6% and 84%, respectively, did not achieve the recommended blood vitamin D concentration of 75 nmol/l. Only 1.3% of the total had serum 25(OH)D concentrations higher than 125 nmol/l. Supplement users had significantly higher serum 25(OH)D concentrations compared to non-users.
The researchers commented that although vitamin D supplement use showed benefits in terms of vitamin D status, at present rates of usage (17.5% of Irish adults), it only has a very limited impact at the population level. Food-based strategies, including fortified foods, need to be explored. Vitamin D status in populations living at latitudes above 40°N is lowest during winter, when the capacity for UVB sunlight-induced dermal synthesis of vitamin D is greatly reduced or even not possible at all.