Now that sweater weather has arrived for much of the country, working to keep up vitamin D levels becomes even more important. After all, the sunshine vitamin is not only important for bone health but has also been tied to a lower risk for certain cancers, heart conditions
That said, where you get your vitamin D matters. Researchers from Australia and the United Kingdom reported in the American Journal of Clinical Nutrition (July 2017) that when study volunteers received 600 IU of vitamin D daily via fortified juice or biscuits for 3 months, vitamin D3—the form found in animal foods like fish and eggs, as well as some supplements—was nearly twice as effective at raising blood levels of the nutrient than was vitamin D2, a plant-based form typically used to fortify vegan foods like dairy-free milk and vegetarian-friendly supplements.
A separate study, published in the European Journal of Clinical Nutrition in 2015, discovered that after supplementation stopped, vitamin D levels declined less rapidly when participants had been taking D3 than when D2 was the supplement of choice. The upshot is that those relying on vitamin D2 to keep up their levels during the winter gloom will likely need more of it than those who get their fill from vitamin D3.