Seize the D - Nourish: plant-based living

Seize the D

Vitamin D is not a nutrient you want to overlook.

Almost everyone knows that we ‘get’ vitamin D from the sun. And the truth is, we really don’t need much to get by on. In fact, it’s estimated that as little as a few minutes outdoors each day during the summer months and more like three or so hours a week during winter will provide enough vitamin D for our bodies to function normally. Yet, many people become deficient. Let’s learn more about this essential nutrient and how to avoid a deficiency.


The term vitamin D actually refers to a collection of naturally occurring chemicals that are derived from cholesterol. The precursor to vitamin D is called 7-dehydrocholesterol, which is converted to vitamin D3 when exposed to ultraviolet B (UVB) light in the skin. Basically, we need sun exposure in order to make vitamin D (unless we consume it directly, but more on that shortly). Vitamin D3 undergoes its final processing in our kidneys to become calcitriol, which is the active form of the vitamin. Phew, it’s a complex vitamin!

Vitamin D basically has one function in the body – but it’s a big one. It enables the absorption of calcium in the gut. A deficiency equates to inadequate calcium absorption and since calcium is crucial for the normal function of muscles, nerves, the immune system, and brain function (among other things), the body has a system to deal with inadequate absorption. Low levels of calcium in the blood trigger the parathyroid glands in the neck to release parathyroid hormone. This, in turn, triggers the bones to ‘release’ calcium, thus somewhat restoring the balance. The problem is that, over time, the bones can lose so much calcium that they can become brittle. Or in other words, osteoporotic.

Osteoporosis is such a major problem in our society that doctors actively seek to identify those susceptible to it and start medical treatment as early as possible. People with osteoporosis are prone to crush fractures of the spine as well as non-traumatic fractures of the hips and long bones. These fractures are significant and are well-known to be associated with loss of independence, institutionalisation, and premature death, especially as people age. Women are particularly prone to osteoporosis after menopause; however, people who smoke or have gut or liver issues are just as likely to develop the condition.


By way of statistics, even in a relatively sunny country such as Australia, the rate of vitamin D deficiency is between 23 and 30 percent of the population. This proportion fluctuates throughout the year but is highest in the winter months. Despite our sun-loving lifestyle, it seems we’re no better off than those in the United Kingdom, where one person out of every three is vitamin D deficient. Unfortunately, the long-term consequences of vitamin D deficiency are not only an increased risk of osteoporosis, but also an increased risk of cancer and a decreased life expectancy.

Apart from osteoporosis and related fractures, vitamin D deficiency has more recently been associated with a range of serious, life-threatening illnesses. It’s interesting to note that in two studies, the Nurses’ Health Study and the Health Professionals Follow-Up Study, higher vitamin D levels (before a diagnosis of colon cancer was made) were associated with a significantly higher overall survival. It is now thought that this is because most colon cancer cells have vitamin D receptors and when vitamin D binds to these, several beneficial things occur. These include death of cancer cells, a reduction in the potential of the cancer to spread, inhibition of new blood vessel growth (which is a key part of cancer growth), and reduced cancer cell division. It has also been suggested that vitamin D can inhibit (oestrogen receptor positive) breast cancer growth.

While the sun-smart campaign has been critical in reducing the prevalence of skin cancer, it has had the unfortunate side effect of reducing our vitamin D levels. So, as the rate of deficiency is growing in Australia, it’s important to be aware of the signs and symptoms of deficiency. If you happen to suffer from frequent illness, fatigue or tiredness, joint or back pain, depression, impaired wound healing, unexplained hair loss or muscle pain, a test for vitamin D deficiency is highly advisable.

As a GP, I prefer to test people’s vitamin D levels at the end of summer because if they’re low then, they’ll definitely be low during the colder months of the year! We consider someone with a vitamin D level of around 70 nmol/L at the end of summer to be susceptible to deficiency because under 50 nmol/L is considered insufficient. Maintaining a vitamin D level greater than 50 nmol/L was found, in a study of over 400 people suffering from knee osteoarthritis, to improve both knee structure (such as increased knee cartilage volume) and reduce symptoms.


Given how important vitamin D is to our health, we need to make sure we maintain adequate levels. Here’s my top tips for keeping those levels up.


If you smoke, work indoors, are approaching or have gone through menopause, have dark skin, have digestive or liver issues, or simply don’t get much sunshine – see your GP and get your levels tested. As mentioned previously, the test is most telling at the end of summer when your levels should be at their peak.


In summer, all it takes is about 10 minutes or so in the sunshine each day with hands, forearms, and face exposed (without sunscreen) to maintain an adequate level of vitamin D. You’ll probably need about three times this amount of time in winter, which admittedly isn’t always easy!


A randomised placebo-controlled trial in 305 community-dwelling people aged 65 years or older found that 2000IU of vitamin D3 per day resulted in an increase in vitamin D levels from 50 nmol/L to 102 nmol/L after 12 months. Accordingly, I recommend 2000IU per day. There is no shortage of vitamin D supplements on the market, and thankfully they don’t require a prescription. However, some types of vitamin D are not vegan-friendly. While vitamin D2 is always suitable for vegans, vitamin D3 can be derived from either an animal or a plant source, so it’s best to check the label. Personally, I use a plant-based vitamin D soft-mist spray each time I brush my teeth, which is also convenient for children. Like many things, the key to success is routine.


Unfortunately, this is a bit easier said than done, especially for those with a plant-based lifestyle. Having said this, it’s possible to get some of the way there through plant sources such as mushrooms (especially portobello and maitake), soybeans, and almonds. Other foods, such as cereals and juices, are often fortified with vitamin D.

Dr Harrison Weisinger

Dr Harry, as he is often called, is a medical practitioner, scientific researcher, and academic with a special interest in nutrition, wellness, and longevity.

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