The Superman’s choice of Vitamin. Unless you’ve been living in the shade (no pun intended) for the last few years, the hot vitamin of the moment is definitely Vitamin D.
This incredible compound was previously only truly noted for its pivotal role in bone health and calcium regulation via parathyroid hormone (PTH). So effective was the discovery of its therapeutic use in preventing the bone-malformation disease ‘rickets’, it prompted administrative action by the UK Department of Health in the 1940s by fortifying everyday foods with the vitamin; with the added benefit of free school milk and a teaspoon of ‘yummy’ cod liver oil for every schoolchild to eliminate this condition (Park, 1940).
As of late though, it has been targeted as the regulator of more than a 1000 vitamin-D responsive genes (Cannell et al. 2009), that may well have multiple implications for a number of clinical conditions, improving body composition and overall sports performance.
THE ‘D-LIGHTFUL’ VITAMIN BROKEN DOWN
Only through the exposure to ultra-violet rays of sunlight (UVB) on the skin and conversion of 7-dehydrocholesterol to cholecalciferol (Vitamin D3) do we obtain the vast majority (between 50% to 90%) of this elite vitamin (Lips, 2010). The rest we obtain from our diet in the form of ergocalciferol (Vitamin D2).
However, it’s not as simple as that.
These two forms of vitamin D are actually inactive compounds. In order to reap the full benefits of this elite vitamin at cell receptor level, they have to be converted to the primary blood-circulating form, calcidiol (25-hydroxyvitamin D) via the liver and kidney.
Once in full circulation, the conversion of calcidiol to the active form of vitamin D, calcitriol (1,25-dihydroxy-vitamin D) at the vitamin D receptor (VDR) level... it can start working its magic.
But I thought exercise = stronger bones?
Though being physically active, in particular resistance and impact training (e.g. running) will naturally increase Bone Mineral Density (BMD) through the loading it places on bone (Rector et al. 2009), it’s a double-edged sword...
Calcium losses in those sweaty gym sessions can be pretty substantial, a typical male could sweat out the equivalent of a glass of milk’s worth of calcium (~100mg) in an intense hour of training with high sweat losses (Martin et al. 2007).
Coupled with a low vitamin D status, the manifestation of even a marginal deficit in BMD has been shown to increase the risk for development of stress fractures amongst hard-training gym-goers, sports enthusiasts and top athletes of all ages (Myburgh et al. 1990; Nattiv et al. 2000; Lovell, 2008).
WELL I DON’T LIVE IN A CAVE, SO SURELY I’M GETTING ENOUGH... RIGHT?
You seriously do not have to be a troglodyte to be deficient in Vitamin D.
UK Dietary Reference Intake (DRI) for adult Vitamin D intake is set at 600 IUs per day, and this is ‘assumed’ to bring calcidiol levels to within the reference range of 20-30 ng/ml with ‘normal’ daily sun exposure.
However, much of the clinical evidence in this area tells a completely different story. A 2003 study by Heaney and colleagues used 67 clinically vitamin-D deficient men who were divided into 4 groups and supplemented with 200, 1000, 5000 or 10,000 IUs vitamin D3 for five months.
Horrifyingly enough, the lowest dose group failed to achieve the reference range for vitamin D even after five months.
Even sportsmen living under the blazing sun of Qatar have been shown to be deficient in this vitamin (Hamilton et al. 2010). Unbeknown to these middle eastern gentlemen, through the intrinsic relationship vitamin D has with calcium status in bone, the authors concluded that this collection of otherwise healthy athletes had shown up to a 60% reduction in bone mineral density`.
Similarly, on more common ground, large cohort studies have indicated that in the ‘sunny’ UK climate vitamin D insufficiency may be as high as 47% amongst adults (Davies & Shaw, 2011).
One contributing issue to this deficiency is that cholecalciferol formation plateaus after only 30 minutes in the sunshine and melanin production increases in skin cells, providing a nice golden tan (Holick, 2002). This in-built safety mechanism prevents excessive UV exposure causing vitamin D intoxication and DNA damage in our skin, thus reducing the likelihood of melanoma formation (skin cancer) and the reason why no one has ever keeled over from hypervitaminosis D due to sun exposure.
How nice of our bodies... hardly.
This evolutionary adaptation may have been appropriate 1.8 million years ago when primitive man was scrabbling around in the savannah all day, eating a vitamin D-rich diet and getting whole-body sun exposure day-in, day-out (Hollis, 2005).
Introduce the modern, proverbially cave-like office dwelling of UK shift patterns, night working, glass windows that filter out UV-B, perhaps overzealous sunscreen usage and a poor dietary intake...vitamin D status plummets quicker than a lead balloon.
WHAT ARE THE SYMPTOMS?
Aside from very rare cases of true osteomalacia, a condition associated with a weakening and malformation of bone in adults due to chronic vitamin D deficiency, the symptoms of vitamin D deficiency are often elusive and ambiguous at best. Hence why so many individuals may be deficient but remain unaware.
Table 1 outlines some of the signs that would indicate a poor vitamin D status in those who are active.
Symptoms of Vitamin D insufficiency in Sports Performance
- Reduction in muscle strength/increased fatigue/strength progression plateau (Cannell et al. 2010)
- Low moods/reduced training intensity/depression (Bartoszewska et al. 2010)
- Generalised bone weakness, pain, increased stress fractures incidence (Martin et al. 2007, Larson-Meyer & Willis, 2010)
- Increased upper respiratory tract infections (Cox et al. 2008)
- Exacerbation of inflammatory bowel disorders & infections (Colitis, Crohn disease, etc) (Froicu et al. 2010)
D IS FOR DENSE, STRIATED MUSCLE...
It’s unsurprising that direct evidence between vitamin D status and optimising muscle mass is starting to mount. In the early part of the 20th Century, athletes were reported to be using UVB radiation to gain a performance advantage over their peers (Cannell, 2009).
More specifically though, in recent years, a relationship between vitamin D insufficiency and atrophy of type II skeletal muscle fibres (muscle breakdown) and increased deposition of intramuscular fat has been found (Ceglia, 2009). Vitamin D administration has been shown to literally reverse the effects of muscle atrophy in the elderly and increase strength. (So clearly those athletes were onto something...)
A NATURAL ANABOLIC WEAPON...
At the VDR, calcitriol is in a class of its own when it comes to anabolic activity.
It wasn’t until recent years that the mystery of the VDR was unearthed by various researchers (Peng et al. 2004; Liao et al. 2008) as a full steroid hormone super-family with a number of different growth-promoting effects at the genetic level (genomic effects).
One that many readers will recognise is insulin-like growth factor-I (IGF-I). Released naturally as part of the adaptation to resistance training, due to its potent effects on tissue recovery, hypertrophy and lean tissue maintenance this compound is often administered as an illegal ergogenic aid in sport (Hamilton, 2010). Calcitriol appears to increase expression of this factor at the VDR (Peng et al. 2004) and is thought to play a large role in the rapid growth spurt seen in recovery from rickets (Soliman et al. 2008).
Unfortunately very little research is currently available in athletic populations (Willis et al. 2008). However, if the muscle-building efforts of ‘grandad and co.’ are anything to go by, vitamin D might just be the new creatine monohydrate in your arsenal.
...LESS BODYFAT AND BETTER NUTRIENT PARTITIONING?
Far from stopping at just improving muscle growth at the genomic level, calcitriol has a number of non-genetic (non-genomic) effects that seem to take its physique and performance-enhancing effects to new heights.
Vitamin D has been shown to improve markers of the metabolic syndrome, a pro-inflammatory condition centred on insulin resistance and obesity, that can easily develop into type II diabetes.
It’s recently been shown that calcitriol with adequate calcium intake may reduce the expression of inflammatory cytokines, directly reduces stimulation of pancreatic cells, normalises intracellular calcium levels that modulate insulin sensitivity and even activates fat-oxidising pathways (Ojuka, 2004, Pittas et al. 2004).
So for the sake of a bit more of the sunshine vitamin and some calcium, your body moderates and soaks up glucose more efficiently and burns more fat. A leaner and more muscular body, here we come.
OKAY I’M SOLD! HOW DO I GET ENOUGH?
Before you all become 24-hour sun-worshippers let’s consider the three best ways to approach getting those bloodstreams brimming with vitamin D.
1. Sun Exposure
Do not suddenly go crazy on the sun lounger in an effort to soak up more of the big D!
Skin cancer is a very real threat.
According to the British Skin Foundation (2011) a British life is lost every four hours per year from the effects of skin cancer.
Whilst there’s conflicting research arguing that sun exposure and vitamin D synthesis may even protect against certain types of cancer, with cases on the rise, especially amongst men, current guidance from the National Institute of Clinical Excellence (2011) would suggest:
- Cover up and stay in the shade between the hours of 11.00 am to 3.00 pm.
- Apply a sunscreen that offers UVA and UVB protection every two hours to most exposed areas.
- Re-apply if engaging in water-based activities (e.g. swimming outside).
2. Dietary Intake
Sadly enough, even though modifying one’s diet would be my first point of call to elevate vitamin D intake, there is a lack of foods that feature this super vitamin. I’ve outlined the best sources in table 2.
- Vitamin D Content Common Foods
- Food Source - Vitamin D Content (IUs)
- Cod liver oil (1 tbs) - 800
- Fresh salmon (85 g) - 288
- Tinned tuna (85 g) - 76
- Eggs (1 medium whole) - 14
- Fortified breakfast cereal (27 g) - 22
Source. McCance & Widdowson (2002)
Also you can see, being fat-soluble in nature, vitamin D is found in foods you would normally associate with being oily or fatty.
Cod liver oil is the finest source of Vitamin D. It is, however, a potent source of Vitamin A, which is easily overdosed. So exercise caution if you plan to add this food to your diet and currently take a full-spectrum multi-vitamin and mineral.
Supplementation can provide hope if you do not like the foods presented, or consume them very infrequently.
Now, if you’ve been following closely so far, you’ll have noted that we mentioned right at the start that the major form of vitamin D presented in food sources is Ergocalciferol (Vitamin D2).
This form, according to the research, does not raise calcidiol levels as efficiently as its collaborator Cholecalciferol (Vitamin D3) (Houghton & Vieth, 2006), so you’ll need to dose higher (or eat more food) to get the same effect.
A dose of 1000-2000 IUs of Vitamin D3 has been shown to be a safe and effective for year-round use (Binkley et al. 2009).
For a single vitamin, The D is a truly remarkable micronutrient that appears to deliver monumental health, sports performance and physique-altering benefits the more we delve into its systemic effects on the human body. We’ve seen that the majority of individuals, including those looking to take their physique and performance to the next level are likely to be deficient. Where a deficiency lies, as in all aspects of nutrition, there’s scope to miss out on muscle gains, recovery and performance benefits. Don’t be that person.
To extract the very best from this compound I’d recommend the following three points:
- During as much of the year as possible, follow sun-safe advice but aim to expose yourself to natural light for at least 15 to 30 minutes daily.
- Increase your intake of vitamin D rich foods where possible.
- Consider a Vitamin D3 supplement to top up those levels that diet and sunshine cannot. M&F
Anabolic Scrambled Eggs with Smoked Salmon and Chives
A remix on a British classic to boost vitamin D intake but keep the nutrition in check. Serves 2 (or one hungry person)
- 3 medium, whole eggs
- 3 oz/85 g smoked salmon, chopped into small pieces
- Freshly ground black pepper (to taste)
- 1 tbsp freshly chopped chives
- 1 tsp organic butter
Whisk eggs together in a large bowl. Heat a medium frying pan with the butter on low to medium temperature (do not allow to burn!). On this low to medium heat, gently cook eggs until curds begin to form. Use a flexible spatula to move the eggs around. Just before the eggs are set, stir in the salmon. Remove from heat promptly and sprinkle the chives and black pepper over. Serve with a toasted wholemeal English muffin to top off this British classic.
Nutrition Data per serving (no muffin)
- Calories (kcal) - 162
- Total fat - 10.5 g (of which saturated 3.7 g)
- Carbohydrate - 0.5 g
- Fibre - 0 g
- Protein - 16.1 g
- Vitamin D - 334 IUs
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