“Keep your face to the sun and you will never see the shadows.” Helen Keller
Vitamin D is omnipresent, and there is a lot of inflicting evidence about vitamin D supplementation. We see many observational studies suggest that low vitamin D level is “linked to” or “associate with” bad outcomes. Those studies are cohort or case-control observations that show a correlation between vitamin D levels and many diseases, but those are correlations, not causations.
Of course, many other factors like the exposure to sun, the foods we eat, age or socioeconomic status are also related to both vitamin D levels and health. The only way to see if the correlation is really a causation is to look at the results from prospective randomised controlled trials, but we don’t have many of them.
In one study, researchers were looking at how exercise and vitamin D may affect the falling prevention among older women. This was a randomised double-blind placebo-controlled clinical trial. Participants were divided into four groups: exercise with vitamin D, exercise with placebo, no exercise with vitamin D and no exercise with placebo.
The main outcomes of interest were reported falls, injuries, bone density, physical functioning and vitamin D metabolism. The results have shown that the rates of falls were unaffected by exercise or vitamin D. However falls with injuries differed. In the exercise group, the rates of falls and injuries dropped almost half. Vitamin D, however, had no effect. Scientists concluded that vitamin D improved femoral neck bone mineral density and only slightly increased tibial trabecular density. Exercise, however, increased muscle strength and balance.
The study has proven that vitamin D supplements help improve the way the bones look on a bone scan, but exercises are necessary to decrease the risk of falls and injuries and improve balance and strength. Vitamin D won’t make any difference.
Another newly published randomised controlled trial of vitamin D supplementation enrolled 230 postmenopausal women of the age of 75 years old or younger who had diagnosed vitamin D deficiency but no osteoporosis yet. It seemed that this was a group where vitamin D supplementation would work.
The researchers were looking at three arms: placebo, low-dose supplementation and high-dose supplementation. Women were followed for a year. The results have shown that in the high-dose group calcium absorption went up 1%, in the placebo group it went down 1.3% and 2.0% in the low dose arm. Looking at other outcomes, there was no impact on spine, mean total hip width, mean femoral neck width or total body bone mineral density.
There was no effect on the trabecular bone score, muscle mass, functional tests, physical activity, no changes in falls, not even the number of people who fell. It turned out that supplementation with vitamin D for an actual deficiency of that vitamin had no or minimal effect on bone measurements and outcome.
The third study was looking at the effect of vitamin D supplementation on blood pressure. This was a large meta-analysis, a systematic review and randomised placebo-controlled clinical trials incorporating individual patient data on vitamin D and blood pressure. Both forms of vitamin D (active and inactive) were used as well as analogs.
The scientists analysed 46 trials involving more than 4,500 participants. Vitamin D supplementation had no effect on either systolic or diastolic blood pressure. Vitamin D supplementation didn’t lower blood pressure, and it didn’t protect the elderly, but the exercise did. It’s more challenging to start exercising than to take a pill, but in reality this is what actually works.
How much vitamin D humans need?
We have enough evidence that a shortage of vitamin D is bad for us, but we still don’t know what is the correct level to have.
The Recommended Dietary Allowance (RDA) is about 600 IU of vitamin D a day for people age 1 to 70-year-old and 800 IU for ages above 70. Various studies have shown however that this may not be enough suggesting the maximum of 1,000-4,000 IU a day.
Those who are overweight and obese for example often require more than the recommended dosage to sustain their supplies.
The American Endocrine Society Guideline, recommends 1,500 to 2,000 IU of vitamin D a day, that is not going to come from food.
The Institute of Medicine Committee did a comprehensive and rigorous review based on nearly 1,000 studies of the evidence both bone health and non-skeletal outcomes in relations to vitamin D.
The committee concluded that there was a compelling evidence that vitamin D has a role in maintaining bone health and the recommended dietary allowances mentioned above are based primarily on bone health purposes covering more than 97% of the US and Canadian population.
However for a non-skeletal outcomes like cardiovascular disease, diabetes, autoimmune diseases and cancer the evidence was found to be inconsistent, inconclusive and not yet of high enough quality to really inform the nutritional requirements of vitamin D.
The current recommendations cover people living in various locations, and very cold climates like Alaska where there is not much opportunity for the sunshine for approximately six months of the year.
We have two major natural sources of vitamin D - the foods we eat and the exposure to sunlight. The trouble is that many avoid products rich in vitamin D like plant-based foods or animal products, others are afraid that the sun exposure may cause skin cancer.
The fact that health outcomes improve with vitamin D3 supplementation has been known for a few decades now thanks to research showing that vitamin D3 is actually a hormone.
Although data from many studies doesn’t prove causation, most researchers don't recommend against the supplementation either.