You probably know that vitamin D plays a role in the health of your bones and your immune system, along with reducing the risk of heart disease, cancer, diabetes, and MS. You might also know that low levels are associated with lower testosterone levels and that women with less than adequate amounts of vitamin D prefer to darn socks or can peaches than have sex.
What you might not know, though, is that an impressive number of studies have shown that people who have a high amount of the vitamin in their bloodstream have less fat, more muscle, and more strength.
Scientists at Purdue University wanted to know if overfed rats would fatten up less quickly if they were given extra vitamin D and calcium in their food. Half of the rats were given a lot of sugar and the other half were given a lot of dietary fat.
Further, half of the rats in each group got a sub-optimal amount of vitamin D and calcium while the other half got supra-optimal amounts of vitamin D and calcium.
When supra-optimal amounts of calcium and vitamin D were added to their feed, the rats started to eat more, but the rats got thinner instead of fatter. The scientists theorized that the combo of vitamin D and calcium amped up the fat-burning capability of their mitochondria, along with increasing the production of insulin receptors.
Most Americans already get plenty of calcium, so adding more of it to your diet probably wouldn't aid fat loss. Instead, focus on getting enough vitamin D.
Nutritionists at Mahidol University in Thailand conducted a study on 163 overweight men and women. They found that subjects with higher levels of vitamin D had more muscle and a lower percentage of fat, which they theorize was caused by vitamin D's suppressive effects on the myostatin gene (the more you suppress myostatin, the more muscle you grow).
A report conducted by British sports scientists compiled the results of 6 previous studies that analyzed vitamin D's effects on human strength. The studies comprised 370 men and women between the ages of 18 and 40 who'd taken about 4,000 IU of vitamin D every day. Across the board, the vitamin D users exhibited more strength in the leg press, chest press, bench press, and other measures of strength.
Okay, so maybe you're not deficient. After all, you had a salad with a hard-boiled egg on it last Tuesday and you roll your car window down on sunny days and let UV light manufacture vitamin D from the cholesterol buried in the skin of your hairy forearm.
Fine, but that doesn't mean your vitamin D levels are optimal. Modern living has made it increasingly hard for us to get enough of this crucial nutrient.
We used to get plenty of it from fish, but the farm-raised varieties many of us are forced to eat contain less vitamin D than their wild cousins. There should be plenty of it in dairy, but vitamin D is fat-soluble and most of us eat no-fat or low-fat dairy products. That means the D was removed with the fat. Sure, manufacturers add it back before it goes to store shelves, but unless you ingest some fat with it, your body doesn't absorb the vitamin D.
Lastly, there's the problem with the sun. In order for sunlight to convert cholesterol to vitamin D, you need a UV index of 3 or higher, and the only place you'll find that year-round is near the equator (between the 37th parallels).
So unless you live near Quito, Ecuador, or Pontianak, Indonesia, or are a grizzly bear that snatches wild salmon out of a stream, you should probably take a vitamin D supplement.
Between 1,000 and 4,000 IU a day should do the trick, but you'd need a blood test to really know for sure if you're getting enough. A blood value of 50 ng/ml is considered adequate for health, but for fat-burning and muscle-building purposes, shoot for something around 70 to 85 ng/ml.
- Siddiqui SMK et al. Dietary intervention with vitamin D, calcium, and whey protein reduced fat mass and increased lean mass in rats. Nutr Res. 2008 Nov;28(11):783-90. PubMed.
- Shantavasinkul PC et al. Vitamin D status is a determinant of skeletal muscle mass in obesity according to body fat percentage. Nutrition. 2015 Jun;31(6):801-6. PubMed.
- Tomlinson PB et al. Effects of vitamin D supplementation on upper and lower body muscle strength levels in healthy individuals. A systematic review with meta-analysis. J Sci Med Sport. 2015 Sep;18(5):575-80. PubMed.