Vitamin D3

Vitamin D is a fat-soluble vitamin that is involved in several of the body’s processes. The other fat-soluble vitamins are vitamin A, vitamin E, and vitamin K, and all four of these vitamins can be stored in the fatty tissues of the body. The primary role of vitamin D in the body is to help maintain appropriate levels of calcium and phosphorus. It does this by impacting both how calcium is absorbed from food as well as how the body builds and reabsorbs bone, a process called bone remodeling. Vitamin D’s effects on the bone are due to its activity on cells called osteoblasts (which build bone) and osteoclasts (which reabsorb bone). Vitamin D also plays a role in certain cellular functions, like cell growth, differentiation (the process that allows a cell to do its specific job), and cell death.

Vitamin D can be obtained through food, however very few sources contain it. Animal sources include fatty fish such as salmon, beef liver, and egg yolks. Plant sources include certain kinds of mushrooms. Most food-based vitamin D in the United States comes from foods that have been fortified with vitamin D, which means it is artificially added to the food in a public health effort to help make sure everybody is getting enough each day. Foods that are often fortified with vitamin D include milk, cereal, margarine, orange juice, and yogurt (2).

Vitamin D can also be made by the body when the skin is exposed to direct sunlight. Ultraviolet B (UVB) rays from the sun cause a reaction in the skin, making vitamin D3 out of a type of cholesterol called 7-dehydrocholesterol. It is estimated that only 5–30 minutes of direct sun exposure twice weekly creates adequate levels of vitamin D in the body for most people. Factors affecting how well an individual makes vitamin D from the sun include the time of day/year, the weather, how dark the person’s skin is (how much melanin they have), and whether the person is wearing sunscreen (which blocks UVB). The latitude that somebody lives at is not a good predictor of vitamin D levels. Currently, there are no recommendations regarding how much vitamin D should be obtained from the sun since exposure to UVB can also cause skin damage and cancer. Using sunscreen and avoiding any behaviors that might lead to sunburn are still recommended.

Before it is biologically active, vitamin D obtained from food, supplements, and sunlight needs to change form. First, the liver converts vitamin D to 25(OH)D (calcifediol). Next, the kidneys convert this compound into 1,25(OH)2D (calcitriol). Calcitriol is the active form of vitamin D in the body. Measuring 25(OH)D can be useful to assess body stores of vitamin D, however optimal levels of 25(OH)D and how exactly these levels translate to health have not been well established.

There are a few purported benefits of vitamin D that are either unconfirmed or that do not have enough supporting evidence. These include using vitamin D to prevent and treat diabetes, hypertension, and multiple sclerosis. There has also been conflicting evidence as to whether vitamin D supplementation can improve life expectancy. One analysis initially found that vitamin D supplementation was associated with an improved life expectancy, but a second review of the data (and another subsequent study) did not find this association (2). More studies need to be conducted to better determine whether vitamin D supplementation actually confers any sort of longevity benefit.

Many studies have looked into the efficacy of vitamin D supplementation for the treatment of depression. One review found that, amongst the studies that did not have flaws, vitamin D supplementation is associated with improvement of depression (6).

Vitamin D also has the following health benefits, which is why it was chosen to be an ingredient in the Ro's Testosterone Support supplement:

Testosterone Support

Studies looking specifically at vitamin D’s effects on men are limited. They include the following:

• Erectile dysfunction: One small study found that high levels of vitamin D were associated with high levels of both testosterone and erectile function based on a questionnaire. After supplementation with vitamin D, testosterone levels increased and erectile function improved. Doses used for supplementation were either 1,250 mcg (50,000 IU) or 2,500 mcg (100,000 IU) given weekly, every two weeks, every three weeks, or monthly (7).

• Testosterone: One small study on vitamin D deficient, overweight men undergoing a weight reduction program found that after one year of supplementation with 83.3 mcg (3,332 IU) per day, testosterone levels increased (5).

As a supplement, vitamin D can come as either vitamin D2 (ergocalciferol) or vitamin D3 (cholecalciferol). The biggest difference between these two forms is how they are derived: vitamin D2 comes from plant sources while vitamin D3 usually comes from animal sources. Within the body, both are metabolized in similar ways and many consider them to be functionally equivalent. However, some research has indicated that supplementation with vitamin D3 may be better at raising and sustaining 25(OH)D levels (3,8). There is no difference between getting vitamin D from supplements, food, or sun exposure, as each of these raises 25(OH)D levels in the body (2).

According to the Institute of Medicine and the National Institutes of Health, the Recommended Dietary Allowance (RDA) of vitamin D is 15 mcg (600 IU) per day for men and women ages 1–70. Men and women over age 70 should have 20 mcg (800 IU) per day. However, the Endocrine Society states that supplementation with 37.5–50 mcg (1,500–2,000 IU) per day may actually be more appropriate to maintain adequate blood levels of vitamin D (1). The RDA represents the daily amount of the vitamin that is considered sufficient to maintain bone health in healthy people. On the other end of the spectrum, the Tolerable Upper Intake Level (UL) for vitamin D is 100 mcg (4,000 IU) per day for both men and women over the age of 8 (2).