I've talked in great detail about the role of a sedentary lifestyle and a carb-centric diet in the pathogenesis of insulin resistance, but what about the role of sunlight and vitamin D? One of my interests is trying to uncover why the global burden of insulin resistance weighs so heavily on the shoulders of certain ethnic groups such as South Asians when the whole world is eating unhealthier and is so much more inactive. Studies have shown that South Asians are one of the most sedentary ethnic groups on the planet and our diet weighs heavily in excess carbohydrates, but are those the only reasons why we experience such intense insulin resistance compared to most other ethnic groups? There is another factor I see over and over in the office and it is extremely low vitamin D levels. South Asians naturally inhabited a subtropical zone with abundant sunlight perfusing their skin with UV-B radiation, triggering the synthesis of vitamin D, an essential hormone powering multiple metabolic reactions throughout our body. Our darker skin tone protected us against the ravaging effects of the sun, preventing us from developing the skin cancers commonly seen in fair skinned folks from Northern Europe and other regions distant from the equator. In essence, from an evolutionary perspective, South Asians were designed to toil outdoors in the bright sun and as a result, our primitive ancestors certainly had no issues with vitamin D deficiency.
We'll address multiple conditions associated with vitamin D deficiency in a moment, but I wanted to first explain how sunlight generates solar power for humans. Mitochondria are the power-generating structures in our cells that convert glucose and oxygen into ATP, a primary fuel source for our body. However the process of making energy (ATP) requires energy and our cells use phosphocreatine as its source. For example, the mitochondria in muscle cells feed on phosphocreatine to generate ATP to power muscle contractions. The time it takes to refill precious phosphocreatine stores is a measure of mitochondrial efficiency and this study shows vitamin D levels are correlated with replenishing phosphocreatine. The critical role vitamin D plays in muscle cell metabolism may explain why some of my patients report reduced muscle aches and fatigue after their low vitamin D levels are brought up to an optimal range. This might also be a pathway by which vitamin D improves insulin resistance. More energy-efficient muscle mitochondria means muscles can more readily soak up glucose after periods of exercise, since muscle contractions can increase glucose uptake without the need for insulin. This is a prime example of how vitamin D represents a true source of “solar power” that spurs human movement through fuel-efficient muscle contractions.
Additional Health Risks of Vitamin D Deficiency
Most folks are aware of vitamin D's role in triggering calcium absorption from the intestine, allowing it to build stronger bones, but are relatively unaware of the growing list of other key roles vitamin D plays in orchestrating a variety of metabolic reactions. Vitamin D is in fact more hormone than vitamin because of its myriad effects. Vitamin D deficiency has been linked to everything from insulin resistance (prediabetes, diabetes) and heart disease to cancer, dementia, autism, asthma and depression. Vitamin D has potent anti-inflammatory effects and we know inflammation sits at the center of most chronic health conditions.
The Sun Can't Be Replaced By A Pill
I still marvel at the fact that a star located 98 million miles away has a profound effect on my metabolism via vitamin D production. This is one of the greatest examples of a human being's direct connection and dependence on nature. Despite this, when I inform patients of there low vitamin D, the usual question is “how much vitamin D supplement should I take?” A supplement by definition is meant to be in addition to something else, and in this case that “something else” is some form of regular sun exposure. Just like taking an antioxidant pill is not the same as eating cauliflower seasoned in turmeric, a tiny vitamin D capsule cannot be a complete replacement strategy for our exposure to the center of our solar system. Sunlight, unlike a vitamin D supplement, actually raises levels of beta endorphins in our bloodstream, also know as our feel-good chemicals. Here in Silicon Valley we are on the brink of winter and our precious hours of sunlight are gradually tapering down. Vitamin D and endorphin levels will inevitably dip as many of us will reach work in the dark and leave work in the dark with minimal interim sun exposure. This is a key reason I see higher levels of stress, depression and anxiety during the winter holiday season.
How Much Vitamin D Should I Get?
This is a tough question and there is a lot of conflicting data regarding the optimal vitamin D level and dosage. I've adopted a more recent approach of tailoring the level to an individual patient's risk factors. In my anecdotal experience, along with some supportive evidence, I have noticed improvements in markers of insulin resistance and high blood pressure along with a drop in hsCRP, a marker for inflammation. I will typically aim for a vitamin D level between 40-50 ng/ml in these patients. If I see a relatively healthy patient with no measurable health risks, I aim for a level between 30-40 ng/ml. Some experts aim much higher, but at this point I am not comfortable and am underwhelmed by the existence of strong evidence to support the approach of “higher is better.” So now let's talk about sun dose and supplement dose:
1. Sun Dose: Safe and regular sun exposure, if your geographic location allows it, will give you the metabolic and psychological benefits of natural UV exposure. Dr.Michael Holick, a vitamin D expert, recommends you first find out your “burn time” or minimal erythemal dose (MED). This is the time it takes for your skin to just turn pink. He recommends you spend half of your “burn time” in the sun 2-3 times a week to get a sufficient dose of vitamin D. For example, if your burn time is 40 minutes, then your ideal dose would be 20 minutes 2-3 days a week. Apply sunscreen to your face and keep your larger surface areas (legs, arms, trunk) exposed. Just exposing your arms and legs would mean about half your body surface is exposed. If you sunbathe longer than this, then generously apply sunscreen, especially if you have lighter skin and/or a family history of melanoma.
2. Supplement Dosage: Your daily vitamin D dosage varies depending on various factors. For example, body fat is a vitamin D trap that reduces the amount of vitamin D available to the rest of the body. So the more body fat you have, the higher your dose. There is also individual variability in how we metabolize vitamin D. It's reasonable to start with a standard dosage and then adjust based on your repeat blood levels. If you are severely deficient, you need a higher loading dose first. For example, you may get 50,000 international units (IUs) once a week for 8 weeks followed by 2,000-4,000 units daily as a maintenance dose. I tend to use 2,000 units for my patients with less body fat who are fair skinned and are getting some natural sun exposure and 4,000 units daily for my darker skinned patients who spend very little time outdoors, like my Asian Indian high-tech workers.
3. Dietary Vitamin D: It's not possible to replace vitamin D deficiency through diet alone, but vitamin D rich foods happen to be the ones that are also nutrient dense. This includes foods like wild salmon, eggs, and dairy.
4. Vitamin K2: Vitamin K2 is the lesser known variant of vitamin K which is responsible for directing the calcium absorbed by vitamin D to bones rather than to blood vessel walls and soft tissues. Since heart attack causing plaques contain calcium, vitamin K2 deficiency may be one way in which misguided calcium ends up in arteries rather than bones. This study suggests a reduction in heart disease risk in those consuming dietary vitamin K2. This is a relatively new area of nutritional science with limited evidence, so until larger scale studies are available that prove vitamin K2 supplementation truly reverses atherosclerosis, there is no strong recommendation for taking K2 supplements. Natural sources of vitamin K2 come from foods such as natto (fermented soy beans), hard and soft cheeses, egg yolks, and butter to name a few. I've discussed in prior posts how dairy and egg yolks can be potentially heart healthy foods, and vitamin K2 may be one additional mechanism that explains their protective effect.
5. Vitamin D Apps: The D-minder app allows you to input all the variables we discussed, including your location, season, body size, etc. in coming up with your proper sun exposure time. What I like about this App is it measures your sun derived vitamin D dose in real time. I know the app reviews are not stellar, but I think it provides a much more thoughtful and personalized way of estimating sun exposure time. The Vitamin D calculator app is an app that allows an estimate of vitamin D intake from diet, sun, and supplements.
What About Kids?
Kids were designed to be outdoor creatures, soaking in abundant sunlight while scaling playground structures, riding their bikes around neighborhoods, and digging through their backyards searching for worms. Unfortunately today's mostly indoor bound children are now becoming increasingly vitamin D deficient from basking in the screen light of computers and digital devices, which incidentally does nothing for vitamin D production, but instead disrupts our body's natural sleep-promoting melatonin production. Not only does vitamin D deficiency in children increase the risks of insulin resistance and all the inflammatory health conditions we discussed, it also affects the critical bone and muscle metabolism essential for proper growth and development. In fact many pregnant mothers are vitamin D deficient, which means they lack sufficient calcium stores to ensure proper skeletal growth in the developing fetus. Low vitamin D levels are also associated with autism as found here, and South Asian pregnant mothers are especially at risk given their often severely low vitamin D levels. Vitamin D deficiency is a health crisis affecting every stage of human development. Reconnecting with the sun and vitamin D rich, nutrient dense foods, along with sensible amounts of vitamin D supplementation are key strategies to ensuring optimal physical and mental health for adults and children.