Vitamin D’s effects on bone health is well-known—the Institutes of Medicine’s (IOM) recommendation a decade ago that blood levels of vitamin D be above 20 ng/dl was made strictly for the vitamin’s benefit on preventing the deficiency disease, rickets.
Vitamin D deficiency causes rickets in children and will precipitate and exacerbate osteopenia, osteoporosis and bone fractures in adults.
But vitamin D deficiency has also been associated with increased risk of common cancers, diabetes, hypertension and immune dysfunction.
The IOM's vitamin D recommendation was for a daily intake of 600 IU/day for ages 1-70 years old and 800 IU/day for those older than 71, corresponding to a serum 25-hydroxyvitamin D level of at least 20 ng/ml. That, said the IOM, would meet the requirements of at least 97.5% of the population.
Very few foods naturally contain vitamin D. Chief among dietary sources are fatty fish, egg yolks and liver. One study noted that wild-caught salmon contained between 75% to 90% more vitamin D compared with farmed salmon. Another study found that farmed salmon vitamin D content ranged from 0.7-2.9 mcg—each 100 IU of vitamin D is 2.5 mcg, so a serving of farmed salmon gets you at most only 15% of the daily value for the minimum requirement of vitamin D. That same study found wild salmon ranged from 9.4-18.5 mcg, so about 400-800 IU, which is about the daily value. That’s a huge difference! You have to eat a veritable school of farmed salmon to equate to the vitamin D levels found in a single serving of a proper wild salmon.
Foods that are fortified with vitamin D (milk and cereal chief among them) are often inadequate to satisfy either a child's or an adult's vitamin D requirement.
Sunshine and supplementation
And that brings us to sunshine and supplementation.
On the sunshine front, researchers in Norway calculated that the equivalent of daily doses of 2,000 IU of vitamin D can be attained with 40 minutes per week of whole-body exposure. They simulated this in a sun-tanning booth. (Are they still a thing?) Under normal conditions, like a backyard or a beach or a trail, you’re probably not as exposed to the sunlight as in a tanning booth, so the time needed to approximate 40 minutes in the tanning booth will be more.
As for supplements, while vitamin D by itself is well and good, its activity is optimized with the presence of other nutrients.
Magnesium is needed to activate vitamin D. All of the enzymes that metabolize vitamin D also require magnesium, which acts as a cofactor in the enzymatic reactions in the liver and kidneys. The famous NHANES population study, a sample of 5,000 Americans, found that high intakes of magnesium correlated with reduced risk of vitamin D deficiency. Researchers also found that the link between low vitamin D blood levels and death by cardiovascular disease and colorectal cancer were obviated by magnesium intake—especially if magnesium intake was higher than average. And taking high doses of vitamin D can deplete the body of magnesium, making their combination a good idea.
Vitamin K2. While no studies look at vitamin K status and vitamin D absorption, vitamin K2 is crucial for the beneficial action of vitamin D in the body. Both are fat-soluble vitamins and play a central role in calcium metabolism. Vitamin D promotes the production of vitamin K-dependent proteins, which require vitamin K for carboxylation in order to function properly. Moreover, increasing vitamin D intake increases calcium absorption, particularly when combined with calcium supplementation, and promotes hypercalcemia—too much calcium in the blood. Vitamin K2 can help with this issue because it helps the body place calcium appropriately—out of the arteries where you don’t want it and into bones where you do. “Based on the current research,” said Kate Maresz, Ph.D., who runs the International Science & Health Foundation based in Poland and vitaminK2.org, “there is enough evidence to recommend combined vitamin D3 and K2 supplementation for the prevention of bone fracture and as a support for cardiovascular health.”
Sugar is bad. We all know this. But a provocative animal study found that excessive fructose consumption can inactivate blood levels of 25-hydroxy vitamin D to its inactive form. “This finding is highly significant,” concluded the researchers, “because fructose constitutes a substantial portion of the average diet of Americans already deficient in vitamin D.” When you see fructose, you should go immediately to high fructose corn syrup, which is used all too often in many foods containing caloric sweeteners, from drinks to flavored yogurts, cereals, jellies and more. (But maybe not in the products you wisely stock in your store.) “You may get enough sun and supplements,” counseled Roger Seheult, M.D., from the Loma Linda University School of Medicine at a recent webinar produced by the Organic and Natural Health Association, “but if you have high levels of fructose in your diet it will work against you on a molecular level.”
Fats are good. Vitamin D is a fat-soluble vitamin, so it travels easily through cell membranes. Because it’s fat-soluble, fellow fats will help it along its way. In particular, phospholipids such as the brain-healthy fat supplement phosphatidylcholine (PC) can help solubilize vitamin D. Other research has found that vitamin D can be increased in the blood in the presence of monounsaturated fats such as olive oil, avocados, nuts and seeds as well as beef.
Oddly enough, some research shows that the reverse is so with polyunsaturated fatty acids such as fish oil. The thinking is the vitamin D stays enrobed in the fatty micelle of the PUFAs, or the combination of D and the PUFAs increased the size of the micelle to the point where it was too large to penetrate the lining of the intestinal walls. Despite this, the researchers still noted that some fat is needed to promote vitamin D absorption. And other studies have been equivocal—some found vitamin D given either as a powder or in fish oil had no difference in vitamin D absorption, while another study found oil helped vitamin D absorption.
Aging. Older skin just has less ability to produce vitamin D. One study found that vitamin D production in the skin is reduced by two-fold capacity between ages 20 and 80. “You can’t change your age,” said James DiNicolantonio, PharmD, director of scientific affairs for ingredient supplier AIDP, “but you can change your vitamin D status.”
Obesity. Because vitamin D is fat-soluble, it gets stored in fat compartments. That makes it not used by the body. That means obese people don’t get to use all the vitamin D they might be producing or consuming. This was demonstrated in a study using both sun to have the body produce vitamin D as well as supplemental intake. The results were the same for both groups—lean people had higher vitamin D levels compared to the obese. That means recommending to overweight customers that they should take more vitamin D, along with the above recommendations.