Vitamin D is essential for bone health, and taking a multivitamin complex with it can help improve your overall wellbeing. The recommended daily allowance (RDA) of vitamin D is 400 international units (IU) for children up to 4 years old, 600 IU for people 1 to 70 years old, and 800 IU for people over 70 years old. However, some people may need a higher dose, including those with a bone health disorder or a condition that interferes with the absorption of vitamin D or calcium. Unless recommended by your doctor, it is advised not to take more than 4,000 IU per day, which is considered the safe upper limit. Severe vitamin D deficiency in children can cause growth retardation and rickets, a disease in which bones soften.
Therefore, it is important to ensure that you are getting enough vitamin D in your diet. The Institute of Medicine (IOM), Health Canada, the European Food Safety Authority (EFSA), the Scientific Advisory Committee on Nutrition (SACN; United Kingdom), the World Health Organization, the Endocrine Society and other expert groups have all provided recommendations on how much vitamin D you should take by stage of life as a guide for clinical use. In addition to determining if a lack of vitamin D causes illness, further studies are needed to determine if taking a supplement can reduce these risks. Vitamin D3 can be formed when a chemical reaction occurs in human skin when 7-dehydrocholesterol is broken down by UVB light from the sun or so-called “suntan rays”. For most people, the best way to get enough vitamin D is to take a supplement because it's hard to eat enough through food. Inadequate nutritional status of vitamin D is prevalent worldwide and has been associated with autoimmune disorders, heart disease, fatal cancers, insulin resistance, inflammation, neurological disorders, adverse pregnancy outcomes, and increased mortality risk.
Depending on where you live and your lifestyle, vitamin D production may decrease or be completely absent during the winter months. The main sources of vitamin D are sunlight, fatty fish, egg yolks, fish liver oils, fortified foods and supplements. Data from Dr. NHANES showed that the average intake of vitamin D from foods and supplements in women aged 51 to 71 years was 308 IU daily, but only 140 IU from food alone (including fortified products). Vitamin D deficiency should always be treated and some high-risk patients with malabsorption syndromes, osteoporosis or taking medications that interfere with vitamin D metabolism will benefit from supplementation. Many of the body's organs and tissues have vitamin D receptors suggesting important functions beyond bone health.
A meta-analysis of randomized vitamin D trials found a statistically significant 13% lower risk of cancer mortality in those receiving vitamin D compared to placebo.