What is Vitamin D Good For?
Vitamin D is an essential nutrient for overall health. Our bodies produce vitamin D when our skin is exposed to ultraviolet (UV) rays in sunlight. And vitamin D occurs naturally in some foods, is added to others, and is available as a supplement in the form of a pill or a drop. In order to use vitamin D, our bodies must first process it: first in the liver into 25-hydroxyvitamin D [25(OH)D], also known as calcidiol, and then in the kidneys into 1,25-dihydroxyvitamin D [1,25(OH)2D], also known as calcitriol.
Vitamin D is very important for our health. It helps the gut absorb calcium, and the two together promote bone health and help prevent osteoporosis. It also helps with cell growth, neuromuscular and immune function, and reduces inflammation.
25(OH)D is the form of vitamin D that can be measured in the blood to identify deficiencies. The experts haven’t yet completely agreed on the levels that are associated with deficiency. But they have determined that persons are at risk of vitamin D deficiency if the level of 25(OH)D is below <30nmol/L. This blood test is very expensive in Canada and not routinely done unless there’s a suspicion of a deficiency. Testing should be done in people who are home-bound, those living in a long-term care facility (e.g., nursing home), persons with a medical condition that increases the risk of vitamin D deficiency or insufficiency, and those with osteoporosis, a history of a low-trauma fracture (e.g., fracture after fall from standing), or low blood calcium.
Intake of Vitamin D
Sun exposure
Even though most people produce some vitamin D from sun exposure, in Canada we don’t get enough sun to produce adequate levels of vitamin D. Factors affecting UV radiation exposure and vitamin D synthesis include:
- a person’s age (as we grow older our skin becomes less able to make vitamin D);
- the season (which determines both the hours and intensity of sunlight);
- the time of day;
- cloud cover (clouds reduce UV rays by 50%, shade by 60%);
- smog levels;
- skin melanin content; and
- the use of sunscreen. As we know, science is always evolving: In May, 2019, a British Journal of Dermatology study found an increase of vitamin D in participants during a week of cloudless weather in Tenerife, with a very high UV index, even when sunscreens were used properly and prevented sunburn. Sunscreens are necessary to prevent sunburn and skin cancer but I do not wear them in the early morning or late afternoon when the sun’s rays are less intense. I hope I get my dose of vitamin D for the day this way!
Food
There aren’t many food sources of vitamin D, so Osteoporosis Canada recommends supplementations for adults all year long.
Recommended doses of vitamin D:
- 400 – 1,000 IU daily for healthy adults 19-50 years of age
- 800 – 2,000 IU daily for healthy people over 50 or those younger adults at high risk (with osteoporosis, multiple fractures, or conditions affecting vitamin D absorption)
This table from Osteoporosis Canada lists some good food sources and their vitamin D content:
Food Serving Size IU's per Serving
Swordfish, Baked or Broiled 75 g 761 Salmon, pink, Canned, Drained with solids and bones 75 g 435 Cod Liver Oil 5 mL/1 tsp 426 Salmon (Sockeye), Baked or Broiled 75 g 394 Snapper, Baked or Broiled 75 g 392 Milk (all types) 1 c/250 mL 103-105 Soy Beverage, Enriched 1 c/250 mL 86 Yogurt, Plain, Vitamin D Added 175 g 82-113 Egg Yolk, cooked 2 Large 64 Tuna, canned in water, drained unsalted 75 g 60 Orange Juice, Fortified 1/2 c/125 mL 50 Margarine, fortified 5 mL/1 tsp 25-36 Mushrooms, white 125 mL/ 1/2 c 4
Supplements
In supplements and fortified foods, vitamin D is available in two forms, D2 (ergocalciferol) and D3 (cholecalciferol). Some experts recommend vitamin D3 rather than vitamin D2 because it is the naturally-occurring form and it may be more effective at raising vitamin D levels in our bodies.
The amount of vitamin D in multivitamins varies so read the labels carefully to ensure you’re getting the amount you need. And add up all the sources of vitamin D you ingest in a day to avoid taking too much. Just because some is good for you doesn’t mean 10 times more is even better! It is hard to overdose on vitamin D but very elevated levels of 25(OH)D can cause complications such as high blood calcium levels and can increase the risk of developing kidney stones.
Vitamin D Deficiency
Rickets (softening of the bones during childhood) and osteomalacia (softening of the bones in adults) are less common nowadays since many foods are now fortified with vitamin D. But deficiencies can result from certain diets (dairy allergy, lactose intolerance, ovo-vegetarianism, and veganism), not taking enough supplements, limited exposure to sunlight, poor absorption of vitamin D by the gut, and kidneys that cannot convert vitamin D to its active form.
Who’s at risk of vitamin D deficiency:
- Older adults and persons with dark skin – they have less ability to synthetize vitamin D from sunlight;
- People spending long periods of time (living or working) indoors with consequent limited exposure to sunlight;
- Persons with inflammatory bowel disease, celiac, ulcerative colitis, or Crohn’s Disease – they may have impaired gut absorption of vitamin D;
- People who are obese or who have undergone gastric bypass surgery.
Can we prevent diseases with vitamin D supplementation?
There’s good evidence that vitamin D helps prevent and treat bone-related disorders, but there’s now some conflicting evidence on the role of vitamin D in the prevention of falls and fractures.
Our bone isn’t static: at any given moment old bone cells are being broken down and new ones are being formed. As we age, and especially in women in postmenopause with decreased estrogen levels, the rate of bone breakdown is higher than the rate of bone formation. This can lead to low bone density (weak bones) and osteoporosis (porous bones), which in turn increases the risk of fractures.
Osteoporosis is most often associated with inadequate intake of calcium, but since vitamin D is needed to help calcium absorption into the bones, insufficient vitamin D also contributes to osteoporosis.
Vitamin D was thought to prevent fall and fractures in the elderly but this finding is being contested by the Health Research Council of New Zealand which has been looking at the literature published in the past on the role on vitamin D in fall and fractures. The authors say
Our findings suggest that vitamin D supplementation does not prevent fractures or falls, or have clinically meaningful effects on bone mineral density. There were no differences between the effects of higher and lower doses of vitamin D. There is little justification to use vitamin D supplements to maintain or improve musculoskeletal health…
These results aren’t being accepted by all in the field. Some say that “The results of the new meta-analysis do not contradict the beneficial effects of combining vitamin D with calcium supplementation for older patients”, and that “Bolland and colleagues included studies that used very high bolus doses of vitamin D, which are known to increase the risk of fractures or falls, also biasing the results”.
It is unclear if taking vitamin D supplements reduces the risk of cancer or cardiovascular disease. Dr. JoAnn Manson and her VITAL (VITamin D and OmegA-3 TriaL) research group conducted a trial that examined the effects of 2000 IU of vitamin D3 with or without 1000 mg of marine omega-3 fatty acids compared with placebo in over 25,000 people made up of men 50 and over and women 55 and over. The authors conclude that “Supplementation with vitamin D did not result in a lower incidence of invasive cancer or cardiovascular events than placebo”.
Diabetes is a disease caused by the body’s not being able to produce insulin, or to utilize properly the insulin it does produce, resulting in high blood sugar (glucose) levels. Recently, a study in Brazil suggested that vitamin D may promote insulin sensitivity (the increased ability of the body to utilize insulin) and possibly lower blood sugar levels. In this trial, low levels of vitamin D were not proven to cause diabetes but may play a role in diabetes (type2). According to Dr. JoAnn Pinkerton, former Executive Director of NAMS (North American Menopause Society), my certifying body, “Vitamin D supplementation may help improve blood sugar control, but intervention studies are still needed”.
As a healthcare professional who believes in preventive care, I strive to provide advice based on the latest and most accurate evidence-based medicine, including for vitamin D and your health. With ongoing research sometimes what to recommend isn’t all that clear. For now I follow the advice of the Canadian Osteoporosis Society: “[vitamin D] …It helps build stronger bones by increasing the absorption of calcium. It also improves the function of muscles, which can improve your balance and decrease the likelihood of falling and suffering a fracture.”
Teresa Isabel Dias is a pharmacist and Certified Menopause Practitioner (NCMP) who provides education and support on symptom management for women at work and at home so they’ll feel like themselves again and enjoy a vibrant and productive life.
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References for “Vitamin D and Your Health: What is Vitamin D Good For?”
https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
https://www.thelancet.com/journals/landia/article/PIIS2213-8587(18)30348-6/fulltext
https://www.sciencedaily.com/releases/2019/06/190619130303.htm
