In recent years Vitamin D has come into the limelight as a vitamin superstar, and for good reason. This powerful immune-boosting vitamin is not only crucial for bone health but has wide-reaching health benefits encompassing everything in the body from bones and muscles to the heart, brain, thyroid, reproductive organs, gut and multiple immune functions, among other roles. Emerging research supports the role of vitamin D against cancer, heart disease, fractures and falls, autoimmune diseases, influenza, type-2 diabetes and depression. On that evidence, health care providers have increased their recommendations for vitamin D supplementation according to the Harvard School of Public Health. It’s clear that getting enough vitamin D is vital because it affects the whole body in so many ways. Do you have a Vitamin D deficiency? Where do we get it? Read on to find out.
How Common is Vitamin D Deficiency?
Before we get to the good stuff, it is important to recognise that Vitamin D insufficiency affects a large percentage of the population the world over. An estimated 1 billion people worldwide, across all ethnicities and age groups, have a Vitamin D deficiency. This may be due to our modern lifestyle, spending most of our daylight time indoors (at work or in school), as well as environmental factors such as air pollution which also reduces sunlight exposure. In Hong Kong the percentage of those with vitamin D deficiency might be even higher than in other countries owing to these lifestyle and environmental factors. Why is this so important? For the sake of public health in the general population, Vitamin D is a sole risk factor for total mortality.
Hong Kong Vitamin D Status – Infants, Adolescents and Young Adults
A pilot study done on infants born in Hong Kong suggests that Vitamin D deficiency may be prevalent in local Chinese infants at 3 months of age. Among exclusively breastfed infants, 97.4% had Vitamin D deficiency; the rate is higher than that reported in other studies (ranging from 6% to 81%). At 3 months of age, Vitamin D reserves may be used up and infants are not yet taking in solid foods. A lack of sun exposure may also help explain why these exclusively breastfed infants had a high prevalence of Vitamin D deficiency. In these cases, supplementation is required. As babies get older and have a more diverse dietary intake and more sunlight exposure, Vitamin D status may improve. More studies are required to evaluate the natural change in Vitamin D status during infancy.
Among adolescents and young adults in Hong Kong, the data shows a great deal of Vitamin D insufficiency and deficiency. In young adults (age 18 – 26), the deficiency rate was 72% while 76.1 % of adolescents in another study were classified as insufficient or deficient. The lack of sufficient levels of Vitamin D was cited as a risk factor for diabetes and cardiovascular (‘cardiometabolic’) disease in the study on young adults. In the study on adolescents, a significant correlation was found between Vitamin D levels and bone density/bone quality factors.
In particular, one study closed by stating that the data supports Vitamin D deficiency as a modifiable risk factor for cardiometabolic disease and thus, increased Vitamin D intake may alleviate the risk profile.
Vitamin D and the Flu
Vitamin D deficiency in the winter months may be the seasonal stimulus that triggers influenza outbreaks. Results from a randomised, controlled trial in Japan showed that children given a daily Vitamin D supplement of 1200 IU had a 40% lower rate of influenza type A compared with those given a placebo.
How Much is Enough Vitamin D?
Current studies suggest that we may need more Vitamin D than what is presently recommended to prevent chronic disease. If you’re at risk of having a deficiency (many of us are), measuring your level of Vitamin D (serum 25-hydroxyvitamin) will tell you. From there it’s easier to determine how much more you’ll need. Since there are so few food sources and most of us don’t get enough UVB rays from the sun, supplementation may be the answer.
After previous recommendations were published, several of the world’s leading Vitamin D researchers wrote new guidelines. With the purpose of increasing Vitamin D into the sufficient range, these are the amounts they endorse.
- Infants (0-1 year): At least 1,000 IU/day
- Children and Adolescents (1-18 years): At least 1,000 IU/day
- Adults (19+ years): At least 1,500 – 2,000 IU/day
Based on your current levels, you would want to take in enough to avoid insufficiency. The US Endocrine Society provides the following cutoffs:
- Deficiency: ≤ 20 ng/mL
- Insufficiency: 21-29 ng/mL
- Sufficiency: ≥ 30 ng/mL
In case you’re worried about taking too much, the Mayo Clinic cites rare toxicity when 60,000 IU per day is taken over a period of months. In other words, it’s very unlikely.
Sources of Vitamin D
According to Ashley Jordan Ferira, Ph.D., RDN, Director of Scientific Affairs at mindbodygreen, Vitamin D is obtainable via several unique routes: through the skin with adequate UVB/sun exposure, a small handful of natural food sources, some fortified foods, dietary supplements and even prescription drugs.
The Few Foods That Naturally Contain Vitamin D Include:
- egg yolk
- certain fatty fish such as sardines, herring, tuna, mackerel, salmon
- fish liver oil
- UV-treated mushrooms
- fortified foods (only offer minimal amounts)
How Much Sun Exposure is Helpful:
- UVB is best during the hours of 10am to 3pm
- In spring, summer and autumn, 10 – 15 minutes of exposure (over arms and face, or arms and legs/hands) from 10am to 3pm can produce adequate vitamin D in light-skinned populations.
- For older individuals and those with darker skin, more exposure is needed for vitamin D synthesis
- Asians from the Indian subcontinent may require 3 times as much sun exposure as Caucasians, whereas Africans may need 6–10 times more.
It’s important to note that season, time of day, cloud cover, air quality and sunscreen use affect sun exposure and Vitamin D synthesis. Also, UVB radiation does not penetrate glass, so exposure to sunshine indoors through a window does not produce Vitamin D.
Vitamin D Supplements
Without enough sun exposure or food sources, Vitamin D supplementation is a solution. Dr. Ferira refers to Dr. Heaney, who discovered 1,000 IU/day of Vitamin D would raise your levels by about 10 ng/mL, depending on a few other factors. This information can be used to roughly calculate vitamin D supplementation needs. Talk to your doctor about how much you should be taking.
For my own family, I buy a Vitamin D spray or drops (from iHerb or a pharmacy) and add it to the morning smoothie or just have the kids take it straight up. The drops or sprays are typically in an oil base which helps with absorption since Vitamin D is fat-soluble.
Without sifting through piles of research studies or reading countless articles on the topic, I can recommend a fairly comprehensive podcast, called “The mindbodygreen Podcast,” that will have you informed in about 40 minutes. Have a listen when you next go out for a walk or while taking the bus across town.