Currently, in medical circles, vitamin D is the talk of the town.
Produced in our skin on contact with sunlight, it plays a myriad of roles in the human body.
In the past few months, Medical News Today have covered a wealth of research into the group of fat-soluble secosteroids more commonly known as vitamin D.
For instance, recent studies have found that vitamin D might protect against heart failure, diabetes, and cancer, and that vitamin D deficiency causes hair loss.
Vitamin D is completely different than most other vitamins.
In fact, it’s a steroid hormone produced from cholesterol when your skin is exposed to the sun.
For this reason, vitamin D is often referred to as “the sunshine vitamin.”
However, sun exposure rarely provides adequate vitamin D, making it necessary to obtain it from supplements or your diet.
The main function of vitamin D is to help the body absorb calcium and phosphorus in the small intestine. Calcium is needed to support bone mineralization (hardening of bones), cell functions, and proper nerve and muscle function.
People who have a vitamin D deficiency may develop soft, weakened, and brittle bones, a condition known as rickets in children and osteomalacia in adults. Vitamin D is promoted by mainstream clinicians for its role in balancing calcium and phosphorus and for bone health.
The evidence on vitamin D for overweight or obese adults is mixed. According to a study published in Nutrition Journal, 25 mcg daily of vitamin D for 12 weeks in overweight and obese women induced a statistically significant reduction in fat mass compared to those taking a placebo.
Conversely, a 2013 study in Clinical Nutrition examined 4000 IU of vitamin D daily plus resistance training for 12 weeks and failed to find significant changes in fat mass in those taking vitamin D.
There may be a genetic component to this. Evidence suggests that people with a genetically higher body mass index (BMI) tend to have lower vitamin D status .
Despite the association between low vitamin D levels and obesity, scientific evidence does not support a cause-and-effect relationship. A systematic review and meta-analysis of 15 weight-loss intervention studies that used caloric restriction and/or exercise, but not necessarily vitamin D supplementation or other treatment, found that people who lost weight had a significantly greater increase in serum vitamin D concentrations than those who maintained their weight . The authors commented that the cause of this finding might have been stored vitamin D in body fat and skeletal muscle that was released during weight loss. In another study, 400 IU/day vitamin D and 1,000 mg/day calcium supplementation slightly, but significantly, reduced weight gain compared to placebo in postmenopausal women, especially those with a baseline total calcium intake of less than 1,200 mg/day . However, according to a meta-analysis of 12 vitamin D supplementation trials (including 5 in which body composition measurements were primary outcomes), vitamin D supplements without calorie restriction did not affect body weight or fat mass compared to placebo . Overall, the available research suggests that consuming higher amounts of vitamin D or taking vitamin D supplements does not promote weight loss.
Vitamin D has multiple roles in the body, helping to:
- Maintain the health of bones and teeth.
- Support the health of the immune system, brain, and nervous system.
- Regulate insulin levels and aid diabetes management.
- Support lung function and cardiovascular health.
- Influence the expression of genes involved in cancer development.
Vitamin D plays an integral role in bone metabolism. In addition to increasing calcium absorption, vitamin D is also involved in the metabolism of phosphorus, another key mineral that supports bone health. According to one study in the Journal of Mid-life Nutrition, low levels of vitamin D were associated with decreased bone mineral density in women. For this reason, taking a vitamin D and calcium supplement is often recommended for those at risk for bone loss, including postmenopausal women.
Vitamin D plays a role in insulin production and secretion from pancreatic cells .
A study in the Jan. 13, 2004 issue of Neurology indicated that women who get doses of vitamin D that are typically found in daily multivitamin supplements — of at least 400 international units — are 40% less likely to develop multiple sclerosis compared with those not taking over-the-counter supplements.
Despite the fact that some studies have found an association between low blood levels of vitamin D and various diseases, it hasn’t been proven conclusively that a vitamin D deficiency actually causes disease, says Dr. Manson.
For example, a woman with a serious illness may have a vitamin D deficiency. But that may have developed because she spends little time outdoors being physically active or because she has a poor diet, both of which are risk factors for many diseases, as well as for deficiency, says Dr. Manson. Another issue is that diseases can cause inflammation, which can reduce vitamin D levels in the blood. Obesity, which has its own links to many conditions, can also reduce the amount of vitamin D in the blood because your body stores the vitamin in fat tissue, removing it from the bloodstream, where it would show up on tests. “Thus, a low vitamin D level may be a marker for other conditions, but not necessarily a direct cause of disease,” says Dr. Manson.
Here is how too much vitamin D can affect your body in a negative way.
Overconsumption of vitamin D is known as Hypervitaminosis D. It can lead to hardening of kidneys, heart, blood vessels and the lungs. It also causes the over-calcification of bones.
When levels of vitamin D are too high in your blood, toxicity occurs. You might experience dry mouth, headaches, loss of appetite, nausea, constipation, weight loss, confusion, a metallic taste in your mouth, vomiting and diarrhoea as a result.High levels of vitamin D during pregnancy have an association with an increased risk of food allergy2 in a child within the first 2 years of life.
Taken in appropriate doses, vitamin D is generally considered safe.
However, taking too much vitamin D can be harmful. Children age 9 years and older, adults, and pregnant and breast-feeding women who take more than 4,000 IU a day of vitamin D might experience:
- Poor appetite
- Weight loss
- Heart rhythm problems
- Kidney damage
Vitamin D from both foods and dietary supplements is safe at recommended intakes of 600–800 IU/day for adults . Vitamin D toxicity can cause anorexia, weight loss, polyuria, and heart arrhythmias. It can also raise calcium blood levels, which can cause vascular and tissue calcification. The UL for vitamin D is 4,000 IU/day for adults and children 9 aged years and older .