As the sun in the Northern hemisphere drops toward the horizon and we head towards winter, it is the right time to consider vitamin D supplementation. Vitamin D supplements are generally not necessary during the summer if large portions of the skin are exposed to natural sunlight for ≥ 15 minutes a day. This exposure produces ~10,000 to 20,000 IU of vitamin D3 (depending on latitude). However, as the sun’s rays becomes less powerful due to the increasing angle of incidence in winter, the ability of the skin to synthesise vitamin D diminishes. Research has indicated that maintaining a blood level of 25(OH)D3 above 40 ng/mL (100 nmol/L) is necessary to maintain optimal health. In most cases, 2000 IU of vitamin D3 throughout the winter is enough to achieve these levels. However, blood tests should be taken to confirm this on an individual basis.
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