Is there really data to support that you cant get enough vitamin d from the sun in the latitudes above 35-37 during the winter? it seems the evidence is mixed?

The reality is in upper latitudes people spend more time indoors and have lower blood vitamin D levels than those closer to the equator. Low D levels correspond to higher risk of some afflictions. Exposure to at least 30 min of direct sunlight/day can often activate enough D naturally for many to avoid low levels. Supplamenting D is a simple method to assure good levels.

There are a few basics: get sun exposure, if available, 3-4 times weekly when walking 20-30 minutes. Avoid using sun block ointments. Supplement 2,000-5,000 IU's of vitamin D-3. Check your serum levels, ideal being 50-70 ng/ml.

I tested candidates for life insurance, in the USA, for vitamin D levels and about 90% had lower than normal levels. You may read this publication on Pub Med at: J Insur Med. 2014;44(2):103-9.

Living in the northeast, most patients are not outdoors for the thirty minutes suggested daily. The skin exposure is further reduced by wearing winter clothing (very little sun-exposed skin). Exposure behind glass and plastic surfaces further reduces ultraviolet exposure. Most individuals need vitamin D supplements or vitamin D enriched milk to achieve normative levels.