Time to talk a bit of science, time to talk vitamin D!
In my very first post “Are you what your mother ate?” I gave you an outline of the overall concept of my PhD research and I mentioned how vitamin D levels in the mother are thought to affect the baby’s skeletal muscle development and function. So, today I’m going to focus on this wonderful molecule and why you need to get a regular vitamin D fix!
Vitamin D seems to be a hot topic in science at the moment, so I’m sure you’ve heard of it before. But why is it so important?
What is vitamin D and why is it important for me?
Vitamin D is a fat-soluble hormone that your body needs in order for it to function well and for you to be healthy. Research has shown that vitamin D acts at multiple sites around the body to cause various physiological effects important to us. Some major roles of vitamin D include:
One of the first discoveries for the importance of vitamin D was its role in providing bone health. Calcium and phosphorus are two minerals that are essential for the development of strong bones. Vitamin D helps with the absorption of these two minerals for good bone metabolism and as a result an increase in bone density . If you ever saw the TV adverts for Petits Filous yoghurts, then this explains why they were advertising the combination of calcium and vitamin D in their products!
The levels of vitamin D can impact the brain in various ways. Lower levels at birth have been associated with reduced cortical thickness (the cortex is the largest part of the human brain) and nerve growth. Neurotransmitter expression and consequently dopaminergic signalling are also linked with vitamin D levels, and this means various neurological process such as motor control and memory can be affected . Neurological disorders, for example multiple sclerosis, have also been linked to vitamin D deficiency.
Research suggests that vitamin D enhances the immune system and helps fight off those infections! Various cell types in the immune system are able to synthesize and respond to vitamin D. Without getting bogged down in the complexity of immunology, vitamin D helps in combatting bacterial infections by producing two proteins called cathelicidin and defensins which have antiseptic roles. Vitamin D supplementation has also been found to improve autoimmune diseases .
The role in the cardiovascular system is not so clear. Vitamin D status is thought to be important for cardiovascular health, and epidemiological studies have found an association between vitamin D deficiency and cardiovascular risk. Some studies suggest that vitamin D has protective effects in the cardiovascular system, and higher levels have been associated with a lower risk of coronary heart disease. However, the therapeutic benefit of vitamin D supplementation to treat this specifically has not yet been proven, and so research is ongoing… watch this space! 
Yay finally skeletal muscle – this is what I work on! Like other tissues, various components of the vitamin D signalling pathway have been found to be expressed in skeletal muscle, which in itself suggests that vitamin D plays a role in muscle development and function. Human studies have found that higher vitamin D levels in the blood are associated with an increase in muscle mass, strength, performance and a lower risk of falling [5, 6, 7]. It’s also thought that vitamin D regulates the expression of proteins important for muscle contraction, and therefore muscle force production. Vitamin D supplementation in elderly patients has found to increase the number and size of a specific type of muscle fibre, the type-II fibres , and an increase in muscle strength . So here’s a take home message for you… if you want strong muscles get that vitamin D in you!
How do we get vitamin D?
There are two types of vitamin D: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). Vitamin D is a unique vitamin. It’s pretty cool actually, our bodies can make our own vitamin D but we need a starting point – the sun! Those almighty UVB rays convert a molecule called 7-dehydrocholesterol in the skin to vitamin D3, and exposing our bare skin to the sun is an efficient way of increasing vitamin D levels. But warning! Just a short amount of sun exposure is enough for your body to make vitamin D so be careful and don’t burn!
As it’s the winter months we’re all wrapped up in our knitted jumpers and big scarfs. Unless you have a holiday booked to go and soak up some winter sun in the tropics, we’re pretty much covered up head to toe, and this means no skin exposure to direct sunlight. So how else can you get your dose of vitamin D? Exposure to sunlight is not the only way for our bodies to get vitamin D. We can get it through dietary supplements (I personally love the myvitamins range) and foods such as oily fish, red meat, eggs, cheese and fortified products.
The vitamin D you get from the sun, dietary supplements or the food you eat then gets processed by the liver. The enzyme 25-hydroxylase converts the vitamin D into 25(OH)D, and this is the substance that’s measured when assessing vitamin D levels in the blood. This is then sent to various tissues (particularly the kidney) where an enzyme 1α-hydroxylase converts 25(OH)D into the active form 1,25(OH)2D. It is this activated vitamin D molecule that is then able to bind to its vitamin D receptor in order to perform its roles. You can see the vitamin D biosynthesis pathway below!
Vitamin D deficiency
What if I’m not getting enough vitamin D? Vitamin D deficiency (VDD) is when your body doesn’t have adequate vitamin D. It’s highly prevalent worldwide, with variation across populations. Having VDD can result in impaired bone, neurological, cardiovascular, immune and muscle health as detailed above, so it’s vital that you get your vitamin D fix.
VDD is also very common in pregnancy ((less than 25-50 nmol/L 25(OH)D)) and ranges from 5-70% in pregnant women across many populations. It has been linked to various obstetrical complications, affecting both the mother and baby’s health. So ladies, make sure you’re getting that all important vitamin D in your diet! Or even better, enjoy the sunshine – with caution of course!
So there we are, an overview of why everyone should be mindful of getting enough vitamin D! I’ll be doing another blog post linking all of this back to why I’m researching maternal vitamin D deficiency and the effect it has on the baby’s muscle function. So I’ll let you absorb all of this wonderful information and come back soon with the whole Developmental Origins of Health and Disease (DOHaD) side of it, so look out for that one!
If you want to learn more about vitamin D, then the Vitamin D Council website is a good place to start!
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