What is Vitamin D?

Vitamin D, or widely known as sunshine vitamin, is technically not a vitamin. Because cholecalciferol, or vitamin D3, can be made naturally by the body when the skin is exposed to sunlight. Vitamin D can also be obtained from foods and supplements.

Nowadays, some fortified foods have added with vitamin D, such as, milk, cereal, yogurt, orange juice, cheese, and margarine. Natural vitamin D is also found in cod liver oil, meat, egg yolk, and several fatty fishes, such as tuna, swordfish, salmon, mackerel, and sardines.

Tolerable Upper Daily Intake Levels of Vitamin D

The following are dietary reference intakes (DRIs), tolerable upper daily intake levels of vitamin D, by the US Food and Nutrition Board, Institute of Medicine, National Academies :

Infants (0 to 6 months) => 25 μg (1000 IU)
Infants (7 to 12 months) => 38 μg (1520 IU)
Children (1 to 3 years) => 63 μg (2520 IU)
Children (4 to 8 years) => 75 μg (3000 IU)
As for people aged above 8 years, pregnant women, and breastfeeding mom => 100 μg (4000 IU)

μg = microgram; 1 μg = 40 International Units (IU) ([PDF] ULs for Vitamins and Elements)

Benefits of Vitamin D?

Unlike the safety of vitamin D that we obtained from the Sun exposure, having excessive intake of vitamin D from dietary supplements, may cause toxicity. The following are several benefits of vitamin D:

To promote calcium absorption in the small intestine.
To maintain adequate serum calcium and phosphate concentrations for bone formation, mineralization, growth, and repair.
To improve muscle strength.
To prevent rickets (a disease characterized by a failure of bone tissue to properly mineralize, resulting in soft bones and skeletal deformities) in children, and osteomalacia (a condition which can cause bone pain and muscle weakness), and osteoporosis in adults.
To reduce inflammation and improve immune function.
To prevent cancers, diabetes, osteoarthritis progression, multiple sclerosis, hypertension, and secondary hyperparathyroidism (a disorder in which the parathyroid glands in your neck produce too much parathyroid hormone).

Vitamin D Deficiency

Vitamin D deficiency can occur when the usual intake is lower than recommended levels, for example, the limited of sunlight exposure, especially in the subtropical climate area. Milk allergy, lactose intolerance, ovo-vegetarianism, and veganism, are also associated with vitamin D deficiency.

People with dark skin may also at high risk in developing vitamin D deficiency, due to pigment melanin in dark skin people, will reduce the skin's ability to produce vitamin D from sunlight. The elder people might also experience the same thing as the dark skin people. Due to aging, the skin of elder people cannot synthesize vitamin D as efficiently as when they were young.

Vitamin D deficiency is very common in children with cancer. Recent clinical study had shown that the incidence of hypovitaminosis in pediatric cancer patients was 72%. Early detection and supplementation could benefit to high risk patients. (Helou M, et al. 2013)

Vitamin D and Diabetes

Dietary intake of vitamin D supplementation is associated with reducing the risk of type 1 diabetes in animals. A study aimed to demonstrate whether vitamin D supplementation, or vitamin D deficiency in infancy, could affect the development of type 1 diabetes.

The data of 12,055 pregnant women who gave birth, in 1966, in Oulu and Lapland, northern Finland, were collected and diagnosed the development of type 1 diabetes, in December, 1997. From 10,366 children who were analysed, 81 were diagnosed with diabetes during the study. The study ensured that vitamin D supplementation for infants could help to reduce the incidence of type 1 diabetes. (Hyppönen E, et al. 2001)

Another study aimed to investigate calcidiol, or 25-hydroxyvitamin D [25(OH)D], associated with insulin sensitivity and beta cell function. The study among 126 healthy people living in California, had shown a positive correlation of calcidiol with insulin sensitivity and a negative effect of hypovitaminosis D on beta cell function. Hypovitaminosis D subjects may have higher risk of insulin resistance and the metabolic syndrome. (Chiu KC, et al.2004)

83,779 women without history of diabetes, cardiovascular disease, or cancer, were studied for the development of type 2 diabetes. Vitamin D and calcium intake from diet and supplements was assessed every two to four years. During 20 years of follow up, there were 4,843 incident cases of type 2 diabetes.

The collected data had shown that daily intake combination of >1,200 mg calcium and >800 IU vitamin D was associated with a 33% lower risk of type 2 diabetes. The study suggested that vitamin D and calcium intake will potentially benefit in reducing the risk of type 2 diabetes. (Pittas AG, et al. 2006)

Vitamin D and Cancer

A phase II study was demonstrated to determine the pain associated with prostate cancer bone metastasis, and muscle strength parameters, in respond to vitamin D supplementation. The patients were given 2,000 IU oral vitamin D, daily for 12 weeks. The study concluded that vitamin D supplementation may be a useful adjunct for improving pain, muscle strength and quality of life. (Van Veldhuizen PJ, et al. 2000)

A trial using calcium and vitamin D supplementation was demonstrated among 36,282 postmenopausal women. 18,176 women received daily 1000 mg calcium, and 400 IU vitamin D3 supplementation. The other 18,106 women received a placebo for an average of seven years.

The trial resulted that the incidence of invasive colorectal cancer did not differ significantly between women assigned to calcium plus vitamin D supplementation and those assigned to placebo. (Wactawski-Wende J, et al. 2006)

Another randomized placebo controlled trial was demonstrated the efficacy of calcium supplement, and calcium plus vitamin D, in reducing cancers risk. The trial was conducted among 1,179 healthy postmenopausal women aged 55 years or older.

The participants were randomly assigned to receive either, only 1500 mg calcium supplement, a 1500 mg calcium plus 1100 IU vitamin D3 supplement, or a placebo, everyday for four years. The trial, which was also registered at clinicaltrials.gov (NCT00352170), had concluded that the improvement of calcium and vitamin D nutritional status, was related substantially in reducing all types of cancer risk in postmenopausal women. (Lappe JM, et al. 2007)

Several Clinical Trials of Vitamin D

Vitamin D and Fracture Incidence

A randomised double blind controlled trial was conducted to measure fracture incidence and total mortality by cause. The trial was involving 2,037 men and 649 women, aged between 65 to 85 years.

The participants received either 100,000 IU oral cholecalciferol (vitamin D3), or a placebo every four months for five years. The trial resulted that four monthly supplementation, with 100,000 IU oral vitamin D, may prevent fractures without adverse effects in men and women. (Trivedi DP, et al. 2003)

However, another trial among 5,292 people aged 70 years or older, were were randomly received daily 800 IU vitamin D3, or a 1000 mg calcium, or 800 IU vitamin D3 plus 1000 mg calcium, or a placebo. Two years later, 2,886 participants were still taking tablets, 451 had died, 58 had withdrawn, and 1,897 had stopped taking tablets.

But, the collected data from all participants did not support the calcium and vitamin D supplementation, either alone or in combination, for the prevention of fractures in elderly people. (Grant AM, et al. 2005)

Vitamin D to Prevent Weight Gain

Obesity in the U.S. has increased significantly during the past several decades. Also, the promotion that obesity is considered as a disease, and no longer as the linked source of the death triangle of diabetes, heart disease and cancer. A randomized, double-blinded, placebo-controlled trial was performed to observe the role of calcium in the maintenance of a healthy body weight.

36,282 postmenopausal women, aged 50 to 79 years, were randomized at their first, or second annual visit to receive a dose of 1000 mg elemental calcium plus 400 IU of cholecalciferol, or placebo daily. The trial resulted that calcium plus cholecalciferol supplementation has a small effect to prevent weight gain. (Caan B, et al. 2007)

Metabolic Effects of Vitamin D in Pregnant Women

Recently randomized, double blind, placebo controlled clinical trial was conducted in 48 pregnant women aged between 18 to 40 years old at 25 weeks of pregnancy. All participants randomly received either 400 IU cholecalciferol supplements, or placebo, everyday, for nine weeks.

Nine weeks later, the study had concluded that vitamin D supplementation among pregnant women has beneficial effects on metabolic status. (Asemi Z, et al. 2013)