Vitamin D is well-known for its role in building strong bones. But increasingly, research is revealing the importance of vitamin D in protecting against a host of health problems. Serving a dual role as both a hormone and a vitamin, it is the sun that is the main source of vitamin D with few foods being reliable sources of it. In today’s podcast, I’ll outline the key roles played by vitamin D, profile the growing number of health areas linked to it especially as it relates to immunity, and discuss how you can keep your vitamin D levels up. That last point is especially important in today’s times with self-isolation now trending as 2020’s word of the year.
Vitamin D is different from all the other nutrients in that the body can synthesise it, with the help of sunlight, from a chemical precursor that the body makes from cholesterol. That makes vitamin D not an essential nutrient per se as given enough time in the sun, people don’t need any vitamin D from foods. That’s important to know because there are not many foods that are reliable sources of vitamin D.
Though it’s called a vitamin, vitamin D is actually a hormone. A hormone is a compound made by one part of the body that causes another part of the body to respond. Vitamin D has a binding protein that carries it to its key target organs – most notably, the intestines, the kidneys and the bones. All respond to vitamin D by making the minerals needed for bone growth and maintenance available.
Vitamin D has several important functions. Perhaps the most vital are regulating the absorption of calcium and phosphorus, and helping with normal immune system function. Getting a sufficient amount of vitamin D is important for normal growth and development of bones and teeth, as well as improved resistance against certain diseases.
Bone and muscle health
The most clearly established role of vitamin D is to keep calcium and phosphate levels in balance, and with that comes healthy bones and good muscle function.
Vitamin D is a member of a large and cooperative bone-making and maintenance team composed of nutrients and other compounds. This includes vitamins A, C and K. Along with the hormones parathyroid hormone and calcitonin; the protein collagen; and the minerals calcium, phosphorus, magnesium and fluoride. Vitamin D’s special role in bone growth is to maintain blood concentrations of calcium and phosphorus. The bones grow denser and stronger as they absorb and deposit these minerals to make new bone.
Severe vitamin D deficiency causes impaired bone mineralisation, resulting in the disease of rickets in children and osteomalacia in adults. Osteomalacia results in bone and muscle pains, and an increased risk of fractures. Osteoporosis is a condition similar to osteomalacia, but in this case it causes a decrease in bone mass rather than a change in mix of minerals in the bones, but the end consequence is higher risk of fractures. Having adequate vitamin D in the body to promote optimal bone mineral metabolism and bone density is considered a strong preventive measure in cutting fracture risk.
It is not just healthy bones that vitamin D helps with. Muscle cells have specific receptors for vitamin D in the nucleus, which promotes muscle protein synthesis and muscle growth. Vitamin D deficiency can affect a person’s balance which, if combined with poor muscle strength, puts a person at greater risk of falling.
On that topic then of balance and strength, falls are a serious health concern because they are a major cause of injury and death among the elderly, especially in nursing homes. Because of vitamin D’s limited presence in only a few foods and that the sun is the major source of it, less-mobile individuals such as those in nursing homes are at greater risk of deficiency. Vitamin D deficiency is a recognised independent predictor of falls in older people, with low levels of vitamin D associated with lower-extremity muscle weakness, impaired balance and accelerated loss of muscle mass, strength and physical function. A recent medical review of the effectiveness of interventions designed to reduce falls in nursing home residents concluded that vitamin D supplementation can play an important role in reducing the risk of falls. So, vitamin D not only helps keep bones healthy enough to withstand the impact of a fall but helps to prevent that fall occurring in the first place.
And then there is the growing realisation that vitamin D targets other tissues including cells of the immune system, brain and nervous system, pancreas, skin, muscles and cartilage, and reproductive organs. Because vitamin D has numerous functions, it may be valuable in treating a number of disorders. And here the list of disease candidates is long and includes diabetes, cardiovascular disease, multiple sclerosis, obesity, autoimmune diseases, cancer, respiratory disease and some mental health conditions such as schizophrenia. However, most of the evidence for these roles comes from cell culture, animal, and epidemiological studies, not the randomised clinical trials considered to be more definitive. The field of research is fast-moving so it is hard to determine where the truth lies, but it is possible that vitamin D deficiency, and hence supplementation, has a role in many of those conditions I mentioned and research will continue to grow.
To touch on one area that is the most relevant in the world at the moment, and that is immunity, especially from viral infection particularly influenza. The seasonal nature of influenza outbreaks is one that is not entirely understood by medical researchers. Flu season normally falls in the colder months of the northern and southern hemispheres, rather than at one particular time around the globe. In the days before rapid mass international air travel it could be argued it takes time for influenza to spread between hemispheres, but this theory now has little validity. One interesting theory is that vitamin D could explain some of the connection because influenza is more common in the winter during times of less sunlight and therefore less available vitamin D.
One piece of clinical evidence to support a link between vitamin D and influenza came from studies looking at vitamin D supplementation and the prevention of osteoporosis. These studies showed an interesting finding that people allocated to take vitamin D supplements were three times less likely to report suffering from cold and flu symptoms. Other studies have also seen a correlation between low serum vitamin D levels and higher influenza risk. Adding more weight to the evidence, a purpose-designed clinical trial found that children given a daily vitamin D supplement during winter were 42 per cent less likely to become infected with seasonal flu than those who were given a placebo. Because of differing trial designs and dosage levels, not all such trials have found a positive result. It does though open the door to a potentially effective way to keep the immune system at normal function of people going into the flu season, especially those at greatest risk of being infected.
Of course, how this applies to major global crises we are facing at the moment with coronavirus is unclear. One very recent 2019 systematic review of 25 RCTs did find that vitamin D supplementation appeared to show some degree of protection against acute respiratory infections, but this was mostly in people who were considered very deficient to start with. I’ll link to the study in the show notes https://www.ncbi.nlm.nih.gov/pubmed/30675873 How this research applies to one specific virus, that being SARS-CoV-2 which is the coronavirus that causes COVID-19 no one knows There is already way too much noise and nonsense on the Internet in regards to nutrition at the moment with all sorts of claims of ‘boosting your immunity’ and even ‘curing’ in the face of the coronavirus crises.
To be clear, vitamin D supplements are not some magical protection nor cure for the virus. But if you are faced with extended periods of getting less sun from self-enforced social isolation then it is worth to be mindful that you shouldn’t neglect getting outdoors if you can to get some sun during the day. But if it is difficult and as we’re heading into winter here in Australia, then this is certainly one case where vitamin D supplements may be worth considering. A supplement only needs to contain 5-10 micrograms of vitamin D to meet the recommended daily intake for most people. You may sometimes see the vitamin D content of a supplement given in international units so 400 IU is equivalent to 10 micrograms.
Deficiency
Unlike most other nutrients that we obtain from food, vitamin D is one which is found in only a few foods. Fortunately, we can make all we need from sun exposure, which accounts for more than 80 per cent of the vitamin D in your body. Because the sun is the main source of vitamin D, then many of the people who are at risk of deficiency are so because of limited sun exposure. Vitamin D deficiency is not an isolated condition, and deficiency can be endemic in certain population groups such as:
Foods and Sun
Only a few foods contain vitamin D naturally. Fortunately, the body can make vitamin D with the help of a little sunshine. The sun also imposes no risk of vitamin D toxicity because prolonged exposure to sunlight degrades the vitamin D precursor in the skin, preventing its conversion to the active vitamin.
Prolonged exposure to sunlight does, however, prematurely wrinkle the skin and present the risk of skin cancer, which is so relevant in a country like Australia. Sunscreens help reduce these risks, but unfortunately, sunscreens with sun protection factors (SPF) of 8 and higher also impact vitamin D synthesis. A strategy to avoid this dilemma is to apply sunscreen after enough time has elapsed to provide sufficient vitamin D synthesis. And this time window is very small. For most people, exposing hands, face and arms on a clear summer’s day for five to 10 minutes during the peak UV periods 10 am and 2 pm on most days of the week should be sufficient to maintain vitamin D. So, it is not much time at all. In winter months, people in the southern regions of Australia may require two to three hours of sunlight exposure to the face, arms and hands over the course of a week.
The pigments of dark skin provide some protection from the sun’s damage, but they also reduce vitamin D synthesis. Dark-skinned people require longer sunlight exposure than light-skinned people: heavily pigmented skin achieves the same amount of vitamin D synthesis in three hours as fair skin in 30 minutes. Latitude, season and time of day also have dramatic effects on vitamin D synthesis. Below 40° south latitude in the Southern hemi-sphere (and above 40° latitude in the Northern Hemisphere), vitamin D synthesis essentially ceases for the three months of winter. Areas below 40° south latitude include Tasmania and the whole of the South Island of New Zealand. Synthesis increases as spring approaches, peaks in summer and declines again in autumn. People living in regions of extreme southern or northern latitudes may miss as much as six months of vitamin D production.
Most adults, especially in sunny regions, need not make special efforts to obtain vitamin D from food. People who are not outdoors much or who live in northern or southern regions of the world, or in predominantly cloudy or smoggy areas, should look to consume foods containing vitamin D. Very few foods contain vitamin D, though, with the best sources being fortified margarine, together with fatty fish such as salmon, herring and mackerel, and eggs. Currently in Australia, vitamin D fortification is mandated for margarines and is voluntary for low-fat milk, powdered milk, yoghurt and soy milk.
Mushrooms can be a good source of vitamin D if you know the trick of what to do with them. And that is, give them a chance to sunbake before you eat them. Putting mushrooms out in the sun for a few hours either sliced or gill-side up can see them ramp up the production of vitamin D many fold over which means you’ll reap the benefits.
Research wrap up
Now on to my research wrap up segment where I profile a study that has grabbed my attention during the week. And for this week with the world turned upside turn, it is a simple study on gratitude – and how it applies to making better food choices.
Eating healthier tops the list of many New Year’s resolutions, but despite the best of intentions it is not always easy to do. One very novel approach to help promote positive eating habits is to cultivate positive emotions. One such positive emotion is the practice of gratitude.
Gratitude is a state where a person acknowledges that they have obtained a positive outcome, opportunity, or benefit from an external source such as another person. Grateful people are more likely to have a positive outlook on life, are more likely to be happier, less depressed, more socially connected and even sleep better.
So how could a practice of gratitude affect eating behaviours? To answer this question, a research team divided over 1,000 teenagers into one of four different groups. Each group spent five minutes per week over the course of a month writing about one of four different topics. The topics were: gratitude to someone who helped them with their health; gratitude to someone who helped them with their academics; gratitude to someone who did something kind for them; or a list of their daily activities which served as the control group.
To reinforce the sense of gratitude, the students also spent 30 minutes each week improving themselves in the area associated with their writing area be it health, study or kindness. For those in the gratitude groups, they also were asked to read gratitude testimonials and to write about the cost and benefit of the gratitude they felt to themselves and the person giving it.
Students in each of three gratitude groups reported having healthier eating habits as assessed by a diet questionnaire at the end of the month compared to those who just listed their daily activities. Even three months after the gratitude practice finished, they still had better eating habits. And I’ll link to the study in the show notes https://psycnet.apa.org/record/2018-43016-001
How could gratitude improve food choices? One reason is that the practice of gratitude can lead to decreased negative emotions such as stress, boredom and sadness. These negative emotions can drive a person to make poor food choices as they seek out ‘comfort food’ that can be higher in less healthy nutrients.
Practising gratitude is not a ‘quick fix’ solution for overhauling eating habits, but it is one that can help move a person in the right direction. Because gratitude takes the focus off of ourselves and onto other people, it helps lessen negative emotions and give a more positive outlook to all aspects of life – including a person’s relationship to food.
There is so much happening in the world at the moment that can unbalance even the most resilient person. A modest daily practice of gratitude and kindness may help tip the balance back into ensure you are eating well in these very challenging times for us all.
So that’s it for today’s show. You can find the show notes either in the app you’re listening to this podcast on if it supports it, or else head over to my webpage www.thinkingnutrition.com.au and click on the podcast section to find this episode to read the show notes.
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I’m Tim Crowe and you’ve been listening to Thinking Nutrition.