Three of every four Americans have either shortcomings or borderline vitamin D deficiencies. Yet, Dr. John J. Cannell, MD, head of the nonprofit Vitamin D Council contends that the situation is far worse, “95% of Americans are deficient in vitamin D, that's how big the problem is. . “(1)

This vitamin is a suspect in Seasonal Effective Disorder (SAD) as skin cells create D from reacting to the sun. If your low energy, depression, and insomnia are related to seasonal sunlight changes then you may need to boost your intake of vitamin D.

A 2010 national study found that the likelihood of having depression is higher in people with deficiency in vitamin D compared to people who are deficient in vitamin D. In another study, researchers from the University of Toronto noticed that people who were suffering from depression, particularly those with seasonal affective disorder, tended to improve as their levels of vitamin D in the body increased over the normal course of a year. (2) And vitamin D deficiencies may be a suspect in all sorts of illness. A study in the New England Journal of Medicine found that nearly 60% of patients in the hospital for various conditions had low levels of D in their blood, and almost 25% were severely deficient.

A simple blood test can determine if you're deficient. Have your doctor check your levels by doing a 25-hydroxy vitamin D test.

There are two forms of Vitamin D: D2 (ergocalciferol), which is found in plants, and D3 (cholecalciferol), which the body makes from exposure to the sun and is substantially more potent. 20 to 30 minutes of full body exposure to natural sunlight will produce about 20,000 IU * of vitamin D in the blood stream in about 48 hours, depending on age, skin color, and sun exposure.

Healthy people use about 3,000-5,000 IU of Vitamin D a day so we can clearly get enough Vitamin D from the sun. However, the average person makes only 1,000 IU of Vitamin D as we spend most of our time indoors and slather on the sunscreen and put on sunglasses when we are outdoors.

Vitamin D2, known as vegetarian Vitamin D, is around 70% less effective than D3. You can find D3 in egg yolk, meat, sunflower seeds, and oily fish such as cod, tuna, and halibut, but you could never eat enough to keep up with your bodies needs. (By the way, Vitamin D fortified milk only has about 100 IU per 8-ounce glass.) If you can not get enough natural sunlight then taking a Vitamin D supplement may be your best option.

Suggested Daily Dose – There has been much confusion and misinformation on how much vitamin D one should take. The Endocrine Society, world's oldest and largest organization devoted to research on hormones, released what is being considered the gold standard of vitamin D recommendations: 400 to 1,000 IU for infants less than 1-year-old, 600 to 1,000 IU for older children and teens, and 1,500 to 2,000 IU for adults. (4)

If it's winter time, November through March, and you live north of the 33-degree latitude line, then you may need more – that's basically north of Los Angeles, CA; Dallas, TX; Atlanta, GA; Casablanca, Morocco; Sicily, Italy; Athens, Greece; and Kagoshima, Japan.

Vitamin D deficiencies can increase your risk of cancer, heart disease, osteoporosis, asthma, Alzheimer's disease, and even the common cold and influenza. Also, larger doses of Vitamin D appear to help allergies, back pain, fibromyalgia, type 2 diabetes multiple sclerosis, and vaginal infections.

* IU = International Unit. Where as a gram or ounce is a measurement of weight, IU is a measure of potency. For example, 1000 IU of Vitamin C has a different weight than 1000 IU of Vitamin D.

References:

1. Challem, J. (2011). The Vitamin D Debate. Experience Life . December 2011.

2. Depression and Diet [WWW page]. WedMD . URL http://www.webmd.com/depression/guide/diet-recovery

3. Holick, M. (2007). Vitamin D Deficiency. N Engl J Med , 357: 266-281.

4. Chase, C. (2011). New Clinical Practice Guideline Recommends Dietary Intakes of Vitamin D for Children and Adults at Risk for Vitamin D Deficiency [WWW page]. The Endocrine Society . URL http://www.endo-society.org/media/press/2011/experts-recommend-screening-for-vitamin-d-deficiency-in-at-risk-populations.cfm