Vitamin D in the body acts as both a vitamin and a hormone. We get it mostly from the sun – when UVB rays are absorbed across our skin, they interact with cholesterol and undergo enzymatic reactions in our liver and then our kidneys until it becomes active vitamin D which our bodies can use. Cholesterol is not the root of all evil as previously thought; it is essential for hormone and vitamin D synthesis. The body cannot synthesise vitamin D without cholesterol.
By far the most important function of vitamin D is that it aids in absorption of calcium and phosphorus through our intestines. Pick up any good quality calcium supplement and it will most likely contain vitamin D for this very reason. Hence, vitamin D is essential for bone and teeth health – including preventing bone density conditions such as osteomalacia, osteopenia and osteoporosis – as well as the many other roles that calcium plays in the body.
Vitamin D is also anti-inflammatory and is especially important for maintaining a healthy immune system – it modulates our immune response thereby preventing autoimmune conditions but also colds and flu’s.
How do we check our vitamin D levels?
The only way to know your vitamin D levels is to test it via blood. The optimal level of vitamin D is around the 150mmol/L mark. Many doctors will say that anything over 40-50mmol/L is acceptable, but this is clearly far from the optimum level. Always ask for a copy of your test results and check that your levels are within the optimal range.
As vitamin D is a fat-soluble vitamin, it is not easily excreted from the body in urine like water-soluble vitamins. Hence, it is important to test your levels before supplementing vitamin D. Vitamin D toxicity is not common but is possible.
Adequate vitamin D levels are essential for a healthy pregnancy and levels should be screened prior to conception.
During conception and pregnancy, vitamin D is essential for:
- Implantation of the embryo
- Foetal skeletal and tooth formation and growth
- Gene regulation
- Brain development
- Immune system development and subsequent protection from infection
Deficiency of vitamin D in pregnancy is associated with an increased risk of:
- Miscarriage risk – there is a two-fold(!) increased risk of first trimester miscarriage when vitamin D blood levels are less than 50mmol/L (see more on blood levels below)
- Pre-term birth
- Caesarian (c-section) birth
- Low birth weight
- Impaired foetal development, particularly skeletal, lung and immune development
What are the consequences of low vitamin D levels?
- Insulin resistance – meaning it plays a role in weight gain, obesity, PCOS and diabetes
- Autoimmunity – recent (2022) research shows that vitamin D deficiency increases the risk of autoimmune diseases by 22%(1). This includes conditions such as rheumatoid arthritis, Hashimoto’s thyroiditis, Grave’s disease, Crohn’s disease, ulcerative colitis, type 1 diabetes mellitus, psoriasis, Lupus and multiple sclerosis (MS)
- Low immunity – vitamin D is protective against bacterial and viral infections, including bacterial vaginosis (BV). Some research shows that vitamin D is more effective than the flu vaccine
- Neural development – deficiency increases the risk of autism
- Skin conditions including acne and psoriasis
- Mental health conditions – depression, anxiety, seasonal affective disorder (SAD)
- Obesity, heart disease, cardiometabolic disease, blood pressure
- Fatigue and low energy
- Impaired hormone synthesis
- Cancer risk – some sources say that there is the same cancer risk from being low in vitamin D as there is from smoking two packets of cigarettes a day
Where do we get vitamin D?
Our primary source of vitamin D comes from sun exposure. When UVB rays are absorbed across our skin, they interact with cholesterol and undergo enzymatic reactions in our liver and then our kidneys until it becomes active vitamin D which our bodies can use. Cholesterol is not the root of all evil as previously thought; it is essential for hormone and vitamin D synthesis. The body cannot synthesise vitamin D without cholesterol. It’s important to note that vitamin D synthesis cannot occur from exposure to sun through glass or windows – the UV rays need to come into direct contact with the skin.
Obviously there is concern around sun exposure and skin cancers, especially in Australia. A healthy amount of sun exposure is good for us and provides benefits beyond vitamin D. For example, sunlight stimulates serotonin production and helps regulate our sleep cycle, impacting many of our hormones including melatonin and cortisol. The amount of sun exposure and the time of the day is important; 20 minutes in the morning or the afternoon is plenty to reap these benefits without the risk of doing any harm to skin. UV rays are at their harshest from 10am-4pm, so avoid direct sun exposure then.
We also get some vitamin D from our diets:
- Vitamin D3 (cholecalciferol – the active form) is found in foods such as egg yolks, red meat, oily fish (i.e. sardines, mackerel, herring, salmon) and dairy
- Vitamin D2 (ergocalciferol – the inactive form) is found in foods such as sun exposed mushrooms (that’s right, pop your mushrooms outside to sunbake and they will synthesise their own vitamin D!)
Like vitamins A, E and K, vitamin D is a fat-soluble vitamin, meaning it needs to be consumed with dietary fat in order for our bodies to absorb and utilise it. Thankfully, mother nature knows this, hence all of the food sources of vitamin D3 such as eggs and oily fish are also good sources of healthy fats.
Vitamin D is an essential nutrient and is especially important for women who are pregnant or breastfeeding, children, the elderly and people with darker skin. Natural sunlight exposure and food sources should be top priority, and supplementation can be utilised when blood levels are low upon testing.
When supplementing, the form of vitamin D you take and the dose is incredibly important. Speak with your qualified healthcare professional before dosing – as your dose should reflect your blood test levels and also your unique health picture. There is no one size fits all when it comes to supplementing nutrients.