Sunshine-vitamin: a vital nutrient
Updated: Aug 8, 2022
You probably know the primary source of vitamin D comes from sunlight on your skin. Are you getting enough vitamin D? And why is this vitamin so important?
Read on: symptoms of low vitamin D, when to test, and how to supplement.
In the northern hemisphere above the 37th parallel (Toronto's at the 43rd parallel), we rely on the longer days of summer to absorb sufficient vitamin D. We hit a sweet spot of hot enough and long enough days (the longest being the summer solstice at the end of June) to bare our skin for only a couple months of the year and otherwise must find an alternative source of vitamin D to the sunshine.
Also: note that sunblock reduces your ability to absorb vitamin D!
(*be sun safe, but aim for 10-20min of sun exposure in spring and summer before putting on sunblock, but only go for as long as your skin does not burn - fair skin does not need as long an exposure time as darker skin!)
Hoe to know if you're low in Vitamin D: Have you had your vitamin D levels checked? Low vitamin D has been linked to:
poor immune function (ie. getting sick frequently, or slow recovery),
poor calcium absorption / osteoporosis
When to test your Vitamin D levels: Sufficiency of vitamin D is considered at 75nmol/L, though perhaps 100nmol/L or more is closer to optimal. I like to consider your levels in a seasonal context. If you're at 75 at the end of the summer, what will your levels be by the end of winter?
I find the two most useful times of year to test Vitamin D are around the spring and fall equinox:
1) September: your high point (after maximum chances for sun exposure, you should be easily meeting the optimal ranges), and
2) March: your low point (you still want to be in the 75-100 nmol/L range here).
If your levels are suboptimal at either point, consider adding dietary and supplementary vitamin D through the next 6 months.
Your sunshine prescription: spend 10 to 20 minutes daily with at least 20% of your skin exposed (in spring/summer!) to direct sunlight before you put on your sunblock – please know your own tolerance and don’t get a sunburn! Your absorption of vitamin D from the sun depends on the amount of skin exposed and the duration of exposure. In winter, with minimal skin exposure (closer to 5%), you'd need to be outside over 6 hours a day to convert 1000 IU of Vitamin D. For most of us, that's not practical.
Are there dietary vitamin D sources? Yes! Dietary sources provide vitamin D2, which is converted by your liver to the active bioavailable form, D3. The highest dietary sources are:
Mushrooms: if exposed to sunlight for 20 minutes = 600 IU per 1 cup
Fish: salmon and rainbow trout = 1000 IU per 6-8 oz serving
What affects vitamin D absorption?
Vitamin D levels may be most strongly affected by your magnesium status, as magnesium is required to support the absorption of vitamin D and is easily depleted by stress. Many foods are rich in magnesium (including green leafy veggies, nuts/seeds, and cacao!) though soil quality affects nutrient density in our foods! During a stressful time, it can be helpful to have a magnesium supplement on hand (*there are many forms of magnesium - which I'll discuss in a future post - but note that some will have a loosening effect on bowels, which may or may not be desirable!)
While vitamin D aids the transport of calcium, vitamin K2 helps to direct the calcium/vitamin D complex to be deposited in the bone - instead of calcifying in arteries! So, higher doses of vitamin D should always be paired with K2. And maybe, it's the missing magnesium that's causing you to require higher doses?
Vitamin D is also a fat soluble vitamin (like vitamin A, E and K) - which means it will be best absorbed when consumed with a fat in a meal - think healthy fats like extra virgin olive oil, avocado, nuts/seeds, fish or even grass-fed butter if tolerated. However, to transport vitamin D into the brain, an amino acid derivative called L-carnitine is required - and this comes primarily from red meat, and in lesser amounts from poultry, fish and dairy (whey). Vegetarians and vegans are therefore at highest risk of vitamin D deficiencies, though avocados and some legumes have L-carnitine. If you are struggling with fatigue, lack of focus/attention or poor muscle function, L-carnitine levels may be involved. L-carnitine also helps to lower inflammation by raising the antioxidant glutathione.
How do I choose a vitamin D supplement? It's a fat-soluble vitamin, best absorbed with other fats, so take it with food for best absorption. Here's what I look for:
Liquid form - readily available, tasty, usually cost effective, and reduces the pill burden.
Few ingredients - all you need is a carrier oil - ideally coconut MCT or olive oil
Vitamin "D3" (cholecalciferol), the most bioavailable form,
or a combo with D3-K2
Where do I get vitamin K2? K2, or “menaquinone” comes from bacteria fermentation – fermented foods like natto (soy - or other legumes) provide the MK-7 form, while meat, dairy and eggs provide the MK-4 form. Research suggests the MK-7 form promotes bone building best. More is not always better. If supplementing, stay under 120mcg of K2 daily.
Always consume your vitamin D supplement with a fatty food or meal.
CAUTION: This post is not intended as medical advice. Supplementation recommendations are best made by a medical professional who can take into consideration your whole person. Do not supplement without the advice of your medical practitioner if you have kidney stones. Testing vitamin D levels is always recommended prior to initiating supplementation.