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Using Supplements to Maximize your Ketogenic Diet

Ketogenic Diet > Keto Diet Information

Science shows that the ketogenic diet is an effective way to lower blood sugar in diabetes, control insulin resistance, and optimize cholesterol. One of the most common questions we get from people is how to utilize supplements to further reap the benefits of a carbohydrate-restricted diet. Below we outline some science-backed supplements and reasons you might want to use them in order to optimize your carbohydrate-restricted diet.

About 145 million Americans use nutritional supplements each year—that’s almost one-half of the population. [1]

Fight Triglycerides with Fish Oil Supplements

According to Nutrition Business Journal, Americans spend over 1.2 billion dollars on fish oil supplements per year. But what are they exactly and can they benefit your health? Fish oil supplements are capsules that contain various oils derived from the liver and skin of fatty fish such as salmon, sardines, and mackerel. They are rich on a special kind molecule called omega-3 fatty acids, a polyunsaturated fat which helps protect against heart disease and potentially a variety of other health conditions.

Omega-3 fatty acids come in one of three varieties. The first one is called alpha-linolenic acid (ALA), which is found in foods like canola oil, soybean oil, walnuts, and chia seeds. The other two, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are only found in fatty fish and fish oil supplements.

Omega 3 fatty acids are an essential food; this means that it isn’t naturally produced by the body and you must obtain it through dietary means. Unfortunately, many American don’t get enough of any of these three types of omega-3 fatty acids in their diets.

Recent research suggests that fish oil supplements may lower levels of triglycerides, fat molecules found in the blood that store energy for later use. While they are integral to proper body function, elevated levels of triglycerides are linked to an increase risk of cardiovascular diseases. [1, 2]

In a meta-analysis of 68 studies, scientists examined the impact that daily consumption of 3-4 grams of fish oil had on triglyceride levels in humans. Collectively, the studies included over 2,800 subjects and had an average of 41 subjects. Each study lasted at least two weeks in length and their collective average was nine weeks. All studies were either parallel controlled or crossover controlled- meaning that they were all high-quality intervention studies.

After analysis, researchers observed that regular, daily consumption of fish oil supplements led to an average decrease of 25% in triglycerides in healthy subjects. [3] Subjects with initially higher levels of triglycerides (>200 mg/dl) had a more pronounced reduction in triglycerides after supplementation. [3] Interestingly, they also observed that higher supplementation dosages led to greater reductions in triglycerides. As a result of their findings, the authors of the study stated that:

 it is clear that practical doses of n-3 fatty acids have a significant and probably clinically important effect on serum triglyceride concentrations, especially in patients with elevated levels of triglycerides. [3]

Additionally, smaller research studies show that consuming fish oil supplements may optimize triglyceride levels in young, healthy individuals. In a 2013 study assessing the impact of 3 grams of daily fish oil supplementation on ten healthy young men for 13 weeks, researchers observed a 38% average decrease in triglyceride levels at the conclusion of the trial. [4] Thus, athletes and fitness-conscious individuals can use fish oil supplements to lower elevated levels of triglycerides.

Fish Oil & Keto

One study indicates that fish oil supplements utilized in a ketogenic diet can further optimize triglyceride levels. Earlier this year, researchers recruited 35 overweight subjects between 25 and 65 years old and divided them into two groups. The first group of 18 were instructed to follow a Mediterranean ketogenic diet for four weeks. They had an average age of 56.3 years and mean BMI of 29.34. Researchers instructed the second group of 17 subjects to follow the same ketogenic diet and also take three fish-oil supplements containing omega-3 fatty acids per day. These subjects had an average age of 58.1 years and a mean BMI of 29.17.

At the conclusion of the study, both groups showed significant decreases in triglyceride levels after the ketogenic intervention. However, there was variation between the two groups. The subjects that didn’t regularly take fish oil supplements decreased from an average triglyceride concentration of 237.81 mg/dL to 197.27 mg/dL. This represents a 17% decrease. In contrast, the subjects that regularly took fish oil supplements decreased from an average triglyceride concentration of 230.79 mg/dL to 185.54 mg/dL. [5] This represents a 19.6% decrease. [5] Thus, this means that regularly consuming fish oil supplements leads to a greater decrease in triglycerides.

Both groups showed a significant and similar decrease in BMI and percent fat. Additionally, both showed a decrease in total cholesterol and low-density lipoprotein (LDL) but no significant change in HDL-cholesterol. These findings are in-line with many other research studies on the ketogenic diet. As a result of their findings, the authors concluded that

[omega-3] supplementation improved the positive effects of a ketogenic Mediterranean diet with phytoextracts on some cardiovascular/metabolic risk factors and inflammatory state. [5]

Where to get Fish Oil Supplements

There are over 50 fish oil supplements available for purchase. However, they are highly variable in quality. According to trusted supplement adviser Labdoor, almost 50% of fish oil supplements brands don’t contain the daily recommendation of 500 mg of omega-3 fatty acids. Additionally, some are contaminated with toxins such as mercury.

So, which fish oil supplement should you take? The highest quality one is manufactured by WHC UnoCardio 1000. The most bang for your buck fish oil supplement in terms of cost and overall quality is the Vitamin Shoppe omega-3 fish oil supplements here. The full ranking can be found at the Labdoor website. Each manufacturer provides recommended daily dosages. However, we suggest consulting with your doctor and dietitian to get a proper assessment of what is best for you.

Key Takeaway: Using fish oil supplements in conjunction with the ketogenic diet can help lower your triglycerides, especially if you already have elevated levels.

Recommendation: If blood testing through your doctor or other organization shows that you have elevated levels of triglycerides, taking a daily dose of at least 3-4 grams of fish oil along with a sound ketogenic diet is an effective method to lower them. Additionally, adding 2-3 servings per week of fatty fish might be useful.

Optimize Your Lipids Using Spirulina

Fish oil supplements are research-proven way to lower high triglycerides. But can the peculiar blue-green algae called “spirulina” help you lower triglycerides? Some high-quality research suggests it can do that and also help you lower your LDL cholesterol.

What is Spirulina?

In 1988, NASA deemed spirulina to be a “superfood.” But what is it? Spirulina is a common blue-green algae consumed by animals including humans. It actually isn’t a plant; it’s a bacterium, meaning that it is one of the most primitive species on Earth. It comes in two main species: Arthrospria patensis and Arthrospira maxima. Like plant species, spirulina is photosynthetic, meaning that it produces its own food in the form of sugar using sun’s light.

About 50% of spirulina is composed of complete protein. This means it contains all the amino acids you need. One tablespoon (7 grams) of spirulina contains 4 grams of protein, moderate amounts of fiber, and large quantities of critical nutrients including iron, potassium, and magnesium. [6] Despite being nutritionally dense, spirulina is most commonly sold as a supplement because of it is more expensive than other forms of protein per weight.

The Clinical Significance of LDL Cholesterol

The story behind LDL, or low-density lipoprotein, is complicated. LDL transports cholesterol produced by your liver and cells throughout your body. Unlike HDL cholesterol, LDL molecules move slowly through the bloodstream and are vulnerable to oxidizing agents known as “free radicals.” Once oxidized, LDL can easily burrow itself into the walls of your arteries (called endothelium) and impede cardiovascular function. This triggers an inflammatory response in which white blood cells called macrophages rush to eat up the LDL.

Typically known as the “bad cholesterol” to its healthy counterpart HDL cholesterol, increased levels of LDL cholesterol (LDL-C) are associated with an increased risk of cardiovascular diseases (CVD). [7] Some studies show a strong correlation between LDL cholesterol and the risk of cardiovascular diseases in both men and women. [8] Evidence also suggests that decreasing blood levels of LDL-C reduces the risk of CVD. [9]

In a piece called “The Effects of Carbohydrate Restriction on Cholesterol: A Counterintuitive Relationship,” we discussed other important metrics of heart-health such as LDL particle size and Very low density lipoprotein (VLDL). We discovered that the ketogenic diet lowers LDL particle size and VLDL but increases LDL-C. Is there a way we can lower all three in the ketogenic diet?

The Research

In a research study from 2007, Mexican scientists assessed the effects of spirulina on triglycerides and LDL cholesterol. In their intervention, Torres-Duran et. al recruited 36 subjects (20 women and 16 men) and had them take 4.5 grams of spirulina supplement per day for six full weeks. The subjects were all of Mexican origin, did not have a history of cardiovascular disease or diabetes, and were aged 18-65 years. Furthermore, they had no history of taking medications that impact levels of insulin, blood sugar, cholesterol, or insulin such as statins.

At the end of the study, the scientists extracted blood samples from the subjects and assess their lipid profiles. They noted significant differences in their levels of total cholesterol, LDL-cholesterol, triglycerides, and HDL-cholesterol. More specifically:

  • Total cholesterol decreased from an average concentration of 181.7 mg/dL to 163.5 mg/dL, representing a 10.0% decrease [10]
  • LDL cholesterol decreased from an average concentration of 103 mg/dL to 86 mg/dL, representing a 16.5% decrease [10]
  • HDL cholesterol increased from an average concentration of 43.5 mg/dL to an average of 50.0 mg/dL, representing a 12.6% increase [10]
  • Triglycerides decreased from an average concentration of 233.7 mg/dL to 167.7 mg/dL [10]

All of these changes have a positive impact on cardiovascular health. Additionally, the number of subjects in health clinical zones for these lipids increased substantially. Before the intervention, 26 subjects (78.8%) had total cholesterol levels below 200 mg/dL.

After the intervention, 31 subjects had total cholesterol below 200 mg/dL. The changes in triglycerides were even more significant. Prior to the intervention, 21 subjects (about 58.3%) had triglyceride concentrations below 200 mg/dL. After the intervention, 28 subjects had triglyceride levels below 200 mg/dL

ketographs2-07

Finally, spirulina had a desirable effect on blood pressure. Average systolic blood pressure decreased by 9.2% from 120 mmHg to 109 mmHg. Average diastolic blood pressure decreased 7.0% from 85 mmHg to 79 mmHg. Researchers surmised that spirulina exerts these effects through a water-soluble protein called phycocyanin. Because all of these positive effects associated with spirulina, the authors stated that:

The present results demonstrate that spirulina maxima has hypolipidemic effects, especially on TC and HDL-C values but indirectly on TC and HDL-C values and positive effects on lowering blood pressure [10].

The findings of this study have been supported by three other high-quality research studies. [11, 12] Additionally, a rigorous meta-analysis from earlier this year states that there is a “significant effect of supplementation with Spirulina in reducing plasma concentrations of total cholesterol, LDL-C, triglycerides and elevating those of HDL-C.” [13]

Choosing the Right Brand

If you’re interested in purchase a well-regarded supplement, consider Hawaiian Spirulina Pacifica. Most manufacturers provide a detailed outline on how much spirulina to take and when to take it. You can also buy spirulina in powdered form. Consider throwing it in a cup of water or mixing it into a keto smoothie!

Key Takeaways: Taking spirulina at a moderate dose (4.5 g/day) significantly lowers levels of triglycerides. Additionally, it also lowers total cholesterol, LDL-cholesterol, and blood pressure to a reasonable extent while slightly increasing heart-healthy HDL-cholesterol.

Recommendation: If your triglyceride levels, total cholesterol, and LDL levels are elevated to unhealthy levels, consider taking 4.5 g of spirulina per day.

Sodium & Potassium Supplements

As we have previously discussed in the piece “Ketogenic Diet and Insulin Resistance”, the ketogenic diet is a highly effective way to reduce levels of insulin. This is especially helpful considering that many people in United States and the developed world suffer from type II diabetes, prediabetes, or are at risk for developing type II diabetes. [14, 15, 16]

Insulin has many functions in the body. It lowers blood sugar by signaling fat cells called “apidocytes” to store this sugar as fat for later energy use. Insulin also tells kidneys to hold on to important electrolytes such as sodium and potassium and not excrete them.

Sodium is a naturally occurring mineral that helps your body regulate water levels, blood pressure, and acid-base balance. It is instrumental in regulating electrical signals between nerves and allowing brain cells to function properly. Additionally, it helps support the adrenal glands on top of the kidney in producing many hormones.

If sodium levels are too high or too low, this can lead to long-term damage of key cells and tissues. Potassium also helps with maintaining acid-base balance and controlling the electrical activity of the heart. It is also involved in building proteins, breaking down and using carbohydrates, and maintaining normal body growth.

Because insulin levels go down during a ketogenic diet, your body starts shedding excess sodium and water when you start restricting carbohydrates. While many Americans suffer from high levels of sodium and potassium, low levels of these two salts in the body is also an issue of concern for people on the ketogenic diet due to lower levels of insulin and insulin resistance.

Multiple research studies support the inverse relationship between insulin and levels of salts such as potassium and sodium. [17, 18] As a result, many people on low-carb diets may experience fatigue, lightheadedness, headaches, and constipation.

The best way to get more sodium and potassium is to consciously add them into your diet. Generally, people on the ketogenic diet should consider adding 2-4 grams of sodium per day. This can be accomplished in a variety of ways. Many keto friendly foods, such as eggs and lean meats, are naturally high in sodium. Sprinkling on some salt or eating some high-fat, salty foods such as bacon or making a low-carb chicken soup might be a good solution.

Another tip is to add a bouillon cube into a cup of hot water then drinking it (it’s actually pretty tasty and healthy!). A variety of salt supplements can also be utilized, too. Potassium is a bit trickier to add in. You can’t start forking over high-carb bananas. However, avocadoes are a reliable source. A trusted potassium supplement, such as the affordable “Potassium Gluconate” from most stores, might be a good choice.

It is important to regularly watch your sodium and blood pressure levels, though, so they don’t elevate to the point where they make you unhealthy. Consult with your doctor to get checked on these key figures.

Key Takeaways: Because insulin levels are typically lower in people who consume the ketogenic diet, sodium levels might be lower than desired. It is important to take the proper amount of sodium and potassium to make sure electrolytes are in healthy levels.

Recommendations: If you are concerned about low sodium levels or you know that your sodium levels are low, consider eating sodium-rich keto-friendly foods such as eggs and lean red meats. Supplementation with a bouillon cube or well-respected brands is another option. Be sure to monitor salt and blood pressure to make sure they are optimized.

Magnesium Supplements

Magnesium is an essential nutrient for the body. It is the fourth most common element and usually found at 25 grams in the body. About 50 percent of magnesium in the body is stored in bones and the other half is mostly located in organs and tissues. [19] As a cofactor, it facilitates over 300 reactions in the body. [20] Because of this, it is involved many essential processes such as moderating blood pressure, synthesizing proteins, maintaining nerve and muscle function, and regulating blood glucose.

Recent literature shows optimal levels of magnesium are important for maintaining adequate levels of testosterone and getting proper amounts of sleep. [19, 20] Most dieticians recommend consuming a daily dosage of 320 mg of magnesium for women and 420 mg of magnesium for men. [20]

Magnesium deficiency is fairly common. According to a recent survey study, about 43% of the US population does not meet the USDA dietary intake of magnesium. [21] It is more common among people who consume a low-carbohydrate diet. This is partially because the ketogenic diet has a diuretic impact on the body and increases the excretion of ions from the body.

Additionally, many magnesium-rich foods, such as dark, green, leafy vegetables, seeds, nuts, and cocoa, have moderate amounts of carbohydrates. Low magnesium can lead to fatigue, neurological damage, and muscle cramps among other things. Oftentimes, the symptoms of magnesium deficiency aren’t immediately apparent. Thus, it is important to consult with a proper blood testing facility to learn your results and see where you are especially as you start partaking in a low-carb or ketogenic diet.

In order to deal with magnesium deficiency, you can consume regular amounts of keto-friendly, magnesium rich foods. Some examples are avocadoes, high-fat yogurt, and low-carb nuts. Additionally, it might be helpful to consume high-quality supplements of magnesium. The most trusted brand is “Natural Vitality, Natural Calm.”

Key Takeaways: Magnesium is an essential nutrient in the body with many key functions. Deficiency is common and more prevalent in people who regularly eat a low-carb diet because it increases excretion of ions and many magnesium-rich foods are high-carb.

Recommendations: Consider eating keto-friendly, high magnesium foods such as avocadoes and high-fat yogurt. A trusted, high-quality supplement brand might also be helpful. Use blood testing to regularly check your magnesium levels.

Vitamin D & Ketogenic Diet

Another supplement that might be useful to people who consume the ketogenic diet is vitamin D. Vitamin D is a fat-soluble nutrient that also functions as a hormone in the body. It is found naturally in only a few foods, including fatty fish (i.e. tuna, sardines, mackerel) and certain mushrooms. Many dairy products, such as milk and yogurt, are fortified with vitamin D.

The body does produce high amounts of vitamin D when exposed to the sun directly (i.e. being outside on a sunshiny day). Because of this association, vitamin D is often referred to as the “sunshine vitamin.” Prolonged exposure to the sun, however, can increase the risk of skin cancer. Because it is difficult to find in food, excess exposure to the sun carries some health risks, and health professionals frequently recommend that people take vitamin D supplements at varying doses.

Historically, vitamin D is associated with maintaining bone density and strength. [22] However, more recent research has expanded its list of physiological functions. It helps the body absorb minerals such as magnesium and calcium. [23] Furthermore, it helps the body maintain optimal health of the cardiovascular, neuromuscular, and immune system. [24, 25, 26] Optimal levels of the sunshine vitamin is also crucial for fitness: vitamin D increases muscular power, spurs muscle growth, cuts excess body fat, and may even increase levels of testosterone. [27, 28, 29, 30]

When in the body, the liver converts vitamin D to a usable form called 25-hydroxyvitamin D [25(OH)D], also known as calcidiol. [31] Levels of this molecule in the blood are the best indicator of one’s vitamin D status.

Vitamin D deficiency is very prevalent among the national US population. In a 2011 estimate conducted by the Centers for Disease Control, about 25% of Americans are at risk for vitamin D inadequacy which is defined as having serum 25(OH)D levels between 30-49 nmol/L. [32] Another 8% were at risk for vitamin D deficiency, defined as having serum 25(OH)D levels less than 30 nmol/L. [32] Thus, about one-third of Americans have low levels of vitamin D. [32]

ketographs2-08

Because vitamin D deficiency is prevalent among the general population and people on a ketogenic diet have a more restricted diet, we strongly recommend that people take supplement of vitamin D equivalent to 4000 IU/day. Another alternative to supplementation is to modify your diet. Thankfully, many vitamin D rich foods such as fatty fish and fortified dairy is keto-friendly as well. Additionally, consider spending up to 20 minutes per day in sunshine to maximize absorption of vitamin D.

Key Takeaways: Vitamin D is an important nutrient with many key functions in the body. However, its deficiency is common both in people who do and who don’t consume a ketogenic diet.

Recommendations: If you have low levels of vitamin D in your body, consider taking vitamin D supplements, adding some sunshine into your diet, and eating vitamin D rich foods such as fatty fish.

Learn how using supplements alongside a Ketogenic Diet have both health and medical benefits. Shared via http://www.ruled.me/

List of References

  1. Hokanson, John E., and Melissa A. Austin. “Plasma triglyceride level is a risk factor for cardiovascular disease independent of high-density lipoprotein cholesterol level: a metaanalysis of population-based prospective studies.”Journal of cardiovascular risk 3.2 (1996): 213-219.
  2. Miller, Michael, et al. “Triglycerides and cardiovascular disease a scientific statement from the American Heart Association.” Circulation 123.20 (2011): 2292-2333.
  3. Harris, William S. “n-3 fatty acids and serum lipoproteins: human studies.” The American Journal of Clinical Nutrition 65.5 (1997): 1645S-1654S.
  4. Zulyniak, Michael A., et al. “Fish oil supplementation alters circulating eicosanoid concentrations in young healthy men.” Metabolism 62.8 (2013): 1107-1113.
  5. Paoli, Antonio, et al. “Effects of n-3 Polyunsaturated Fatty Acids (ω-3) Supplementation on Some Cardiovascular Risk Factors with a Ketogenic Mediterranean Diet.” Marine drugs 13.2 (2015): 996-1009.
  6. Khan, Zakir, Pratiksha Bhadouria, and P. S. Bisen. “Nutritional and therapeutic potential of Spirulina.” Current pharmaceutical biotechnology 6.5 (2005): 373-379.
  7. Germano, Giuseppe, et al. “European Guidelines on cardiovascular disease prevention in clinical practice (version 2012).” European Heart Journal 33 (2012): 1635-1701.
  8. Neaton, James D., et al. “Serum cholesterol level and mortality findings for men screened in the Multiple Risk Factor Intervention Trial.” Archives of internal medicine 152.7 (1992): 1490-1500.
  9. Cromwell, William C., et al. “LDL particle number and risk of future cardiovascular disease in the Framingham Offspring Study—implications for LDL management.” Journal of clinical lipidology 1.6 (2007): 583-592.
  10. Torres-Duran, Patricia V., Aldo Ferreira-Hermosillo, and Marco A. Juarez-Oropeza. “Antihyperlipemic and antihypertensive effects of Spirulina maxima in an open sample of Mexican population: a preliminary report.” Lipids Health Dis6.1 (2007): 33.
  11. Mazokopakis, Elias E., et al. “The hypolipidaemic effects of Spirulina (Arthrospira platensis) supplementation in a Cretan population: a prospective study.” Journal of the Science of Food and Agriculture 94.3 (2014): 432-437.
  12. Torres-Durán, Patricia Victoria, et al. “Effect of Spirulina maxima on postprandial lipemia in young runners: a preliminary report.” Journal of medicinal food 15.8 (2012): 753-757.
  13. Serban, Maria-Corina, et al. “A systematic review and meta-analysis of the impact of Spirulina supplementation on plasma lipid concentrations.” Clinical Nutrition (2015).
  14. Noakes, Manny, et al. “Comparison of isocaloric very low carbohydrate/high saturated fat and high carbohydrate/low saturated fat diets on body composition and cardiovascular risk.” Nutrition & metabolism 3.1 (2006): 7.
  15. Volek, Jeff S., et al. “Carbohydrate restriction has a more favorable impact on the metabolic syndrome than a low fat diet.” Lipids 44.4 (2009): 297-309.
  16. Yancy, William S., et al. “A randomized trial of a low-carbohydrate diet vs orlistat plus a low-fat diet for weight loss.” Archives of internal medicine 170.2 (2010): 136-145.
  17. Tiwari, Swasti, Shahla Riazi, and Carolyn A. Ecelbarger. “Insulin’s impact on renal sodium transport and blood pressure in health, obesity, and diabetes.”American Journal of Physiology-Renal Physiology 293.4 (2007): F974-F984.
  18. Chatterjee, Ranee, et al. “Potassium and risk of type 2 diabetes.” (2011): 665-672.
  19. Maggio, Marcello, et al. “The Interplay between Magnesium and Testosterone in Modulating Physical Function in Men.” International journal of endocrinology2014 (2014).
  20. Volpe SL. Magnesium. In: Erdman JW, Macdonald IA, Zeisel SH, eds. Present Knowledge in Nutrition. 10th ed. Ames, Iowa; John Wiley & Sons, 2012:459-74.
  21. Nutrient Intakes Percent of population 2 years old and over with adequate intakes based on average requirement”. Community Nutrition Mapping Project. 2009-07-29. Retrieved2 015-10-16.
  22. Horsley, Tanya, et al. Effectiveness and safety of Vitamin D in relation to bone health. US Department of Health and Human Services, Public Health Service, Agency for Healthcare Research and Quality, 2007.
  23. Ross, A. Catharine, et al. “The 2011 report on dietary reference intakes for calcium and Vitamin D from the Institute of Medicine: What clinicians need to know.” The Journal of Clinical Endocrinology & Metabolism 96.1 (2011): 53-58.
  24. Shils, Maurice Edward, and Moshe Shike, eds. Modern Nutrition in Health and Disease. Philadelphia: Lippincott Williams & Wilkins, 2006.
  25. Wang, Lu, et al. “Systematic review: Vitamin D and calcium supplementation in prevention of cardiovascular events.” Annals of Internal Medicine 152.5 (2010): 315-323.
  26. Hossein-Nezhad, Arash, Avrum Spira, and Michael F. Holick. “Influence of Vitamin D status and Vitamin D3 supplementation on genome wide expression of white blood cells: A randomized double-blind clinical trial.” PLoS One 8.3 (2013): e58725.
  27. Wyon, Matthew A., et al. “The influence of winter Vitamin D supplementation on muscle function and injury occurrence in elite ballet dancers: A controlled study.” Journal of Science and Medicine in Sport 17.1 (2014): 8-12.
  28. Forney, Laura A., et al. “Vitamin D Status, Body Composition, and Fitness Measures in College-Aged Students.” The Journal of Strength & Conditioning Research 28.3 (2014): 814-824.
  29. Pilz, S., et al. “Effect of Vitamin D supplementation on testosterone levels in men.” Hormone and Metabolic Research 43.3 (2011): 223.
  30. Heijboer, Annemieke C., et al. “Vitamin D supplementation and testosterone concentrations in male human subjects.” Clinical endocrinology (2015).
  31. Ross, A. Catherine, et. al. (editors) Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: National Academies Press, 2011.
  32. Looker A.C., C.L. Johnson, D.A. Lacher, et al. Vitamin D status: United States 2001–2006. NCHS data brief, no 59. Hyattsville, MD: National Center for Health Statistics, 2011.

*Written in collaboration with Neel Duggal

 

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