Dr. John MacIntosh, ND, RMT - Naturopathic Doctor
Weak Winter Sun = Low Vitamin D Levels
This time of year, many Canadians are taking vitamin D supplements. And it’s a good thing too. From October to April, the sun’s dim rays are too weak to generate sufficient amounts of this nutrient in our skin, making supplements a virtual necessity.
Low Magnesium = Low Vitamin D Activity
Yet few also know how crucial magnesium is to the normal function of vitamin D. Without sufficient magnesium, vitamin D metabolism simply cannot take place no matter how much active vitamin D3 you take.
Magnesium = Vitamin D ‘Optimizer’
Researchers have also recently discovered that magnesium ‘optimizes’ blood vitamin D levels:
In people with low blood vitamin D levels (often persistently low, in spite of supplementation), magnesium raised ‘D’ levels back to normal
In people with high blood levels (almost always due to over-supplementation), magnesium lowered vitamin D back down to normal levels
Magnesium = Vitamin D’s “Sweet Spot”
Magnesium automatically sets your body at its optimal vitamin D level. This is crucial since most important health benefits of vitamin D (reduced cancer risk) accrue only when blood levels are ideal. Too much vitamin D then, is almost as bad as not enough. (Amer. J. Clin. Nutr., Dec. 2018)
Top Magnesium Food Sources
Magnesium is found mainly in the seeds of plants: beans, peas, nuts, seeds and whole grains. It is also found in leafy greens. Eat a variety of them regularly; we need about 300 mg of magnesium daily.
[Best sources are italicized; numbers indicate grams of magnesium per serving.]
Beans: soybeans/tofu (120-300), black-eyed peas (200), kidney/lima (80), navy (50) [Serving: 1/2 cup, cooked]
Grains: buckwheat (250), whole wheat (140), toasted wheat germ (90), whole/brown rice (80), millet (60), oats/oatmeal (50) [Serving: 2/3 cup, cooked]
Greens: Swiss chard (150), collard greens (70), beet greens (60), spinach (40) [Serving: 1 cup, cooked or raw]
Nuts & Seeds: almonds (100), cashews (90), hazelnuts/ filberts and pecans (80), peanuts (70), walnuts (60) [Serving: 1/4 cup]
Fish: halibut (80) [3oz/100 g]
Sea Vegetables: kelp/nori (80) [Serving: 2 Tbsp./10 g]
Fruit & Vegetables: avocado [1/2 med.], banana [1 med.], potato [1 med., with skin] (all 60)
Whole grains are best eaten closest to their natural state, not hulled or milled into flour first. For example, use grains like wheat berries (whole wheat kernels), toasted wheat germ and cracked (bulgur) wheat as sides or to add nutritional value in baking.
Magnesium-rich, gluten-free choices include brown rice and buckwheat (not a true ‘wheat’, despite its name). Nuts and seeds (lightly- or unsalted) make tasty snacks and salad additions. Try dry roasting grains, nuts or seeds in a pan first before using in cooking. Beans and peas are great in soups, stews, curries and dips, or baked.
How Much “D” Do We Need Per Day?
The Recommended Daily Allowance (RDA) for vitamin D is currently 600-800 International Units (IU) of vitamin D-3 daily. Optimal Daily Intake (ODI) is taken to be 1,000-2,000 IU daily or more, individual needs vary greatly.
Vitamin D-Rich Food Sources
If you don’t eat fish or take fish liver oils daily, I can virtually guarantee you’re not getting enough vitamin D.
Your grandmother was right – the best source of vitamin D is fish liver oil, especially halibut (5,000 IU per teaspoon) and cod (1,000 IU per tablespoon). As for the taste, well ... Thankfully, fish like mackerel and sardines are rich sources of vitamin D (800-1,600 IU per 3 oz/100 g serving). Salmon, trout, tuna and shrimp are other good sources (150-250 IU).
After fish, your best choice is milk, including rice, almond and soy milks because milk is “enriched” with (added) vitamin D, but not much, only about 100 IU per cup. Pork, beef and eggs provide small amounts (<50 IU). For vegans, the best source of vitamin D is mushrooms (especially morels, shiitake and chanterelles) but they provide <100 IU per cup. (Vegans must take vitamins D & B-12 daily.)
Fun In D Sun
The easiest way to get the right amount of vitamin D is to spend time in the direct sun. The ultraviolet (UV-B) rays in sunlight catalyze a reaction in our skin that converts cholesterol into a precursor of vitamin D. Your liver stores any extra until it’s needed, so your body can control how much vitamin D is active at any one time.
Under ideal conditions, fair-skinned folks produce 1,000-2,000 IU of vitamin D in 5-10 minutes of full summer sun (and begin to crisp shortly thereafter), but weaker winter sun produces vitamin D ten times more slowly than summer sun does. Darker, naturally sun-protective skin blocks UV-B so well it can take up to 5 times longer to produce vitamin D.
What About Sunscreen?
Sunscreen of SPF 8 or higher reduces the amount of vitamin D made in the skin by up to 95-99%, as it blocks the UV-B light that drives D’s formation.
Of course, ultraviolet light is also the major cause of skin cancer so definitely use sunscreen, particularly between 10 a.m. and 3 p.m., when UV-B intensity is highest, and especially during summer months.
The new, more sensible recommendation is to put your sunscreen on after you’ve been out in the sun for 20-30 minutes or so.
For good non-toxic sunscreen choices, see Environmental Working Group’s latest list of Best Sunscreens (2018): https://www.ewg.org/sunscreen/
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