Great question Nicky! This is something I go back and forth on myself all the time, as I personally have low Vitamin D levels (I’m from London and live in Boston, so no surprise there), but also working with a dermatologist I understand the harm that too much sun can do to our skin.
Whilst I do recommend everyone who lives in colder climates to supplement with Vitamin D (and its always best to get this tested to establish your baseline levels – test, don’t guess) the amount that is absorbed and used by the body can vary depending on the individual’s gut health and intake of other vitamins that make the D available to the body (Vitamin K, found in kale and broccoli, for example).
The sun is the body’s best source of Vitamin D, and we actually don’t need that much exposure to it to reach our needs. Our faces, necks and chests receive the most sun exposure year round and I feel that these areas should be protected year round with a broad spectrum sunscreen of at least SPF30 or above.
In the Spring and Summer months (i.e.when it is warm enough in Boston) I try to exposure my legs to the sun for between 15-30 minutes a day (depending on the time of day) to increase my Vitamin D levels, but never to the point of going pink, and definitely not red / burning.
Visit your dermatologist once a year as part of your annual health screenings, and track your moles for any changes in size, color, border and texture.