Wintertime is commonly a time when darker moods tend to creep in; a phenomenon linked to a decline in sunlight. Seasonal affective disorder (SAD) affects an estimated 6 percent of the U.S. population, while a milder form, known as the “winter blues,” affects about 14 percent.¹ As noted in the Evening Standard:²

“According to the DSM [diagnostic and statistical manual of mental disorders], people who have SAD are excessively fatigued, lose interest in their hobbies, tend to crave more starches and sweets, may gain seasonal weight, and have difficulty concentrating during darker months.”

That said, longer, darker days tend to influence the behavior of most people, even if you don’t feel outright depressed and depleted. This is because your health and mood are actually intricately tied to exposure to sunlight, even irrespective of vitamin D. For example, your serotonin levels (a hormone associated with mood elevation) rise when you’re exposed to bright light.

Your melatonin level also inversely rises and falls with light and darkness. When it’s dark, your melatonin levels increase, which is why you may feel tired when the sun starts to set (and in the heart of winter, this may be at as early as 4 p.m.). Full-spectrum light therapy, which mimics the natural light from the sun, has been shown to be effective remedy for SAD, and may even be preferable for major depression.

Vitamin D3 supplementation can also be quite helpful for depression and/or the winter blues if you’re vitamin D deficient, which a vast majority are at this time of year. Research shows having a vitamin D level below 20 nanograms per milliliter (ng/mL) may raise your risk for depression by as much as 85 percent, compared to having a vitamin D level greater than 30 ng/mL.

Have You Checked Your Vitamin D Level Yet?

My recommendation is to get your vitamin D level tested twice a year, when your level is likely to be at its lowest (midwinter) and highest (midsummer). This is particularly important if you’re pregnant or planning a pregnancy, or if you have cancer. That means right about now is a good time to get your level checked, to identify your low-point. Based on the research done and data collected by GrassrootsHealth, 40 ng/mL is the cutoff point for sufficiency to prevent a wide range of diseases, including cancer.

For optimal health and disease prevention, a level between 60 and 80 ng/mL appears to be ideal.³ The American Medical Association claims 20 ng/mL is sufficient, but research suggests 20 ng/mL is not even adequate for the prevention of osteomalacia. As for dosage, you need to take whatever dosage required to get you into the optimal range, with 40 ng/mL being the low-end cutoff for sufficiency.

Research⁴ suggests it would require 9,600 IUs of vitamin D per day to get a majority (97.5 percent) of the population to reach 40 ng/mL, but individual requirements can vary widely. If you’ve been taking a certain amount of vitamin D3 for a number of months and retesting reveals you’re still not within the recommended range, then you know you need to increase your dosage.

Over time, with continued testing, you’ll find your individual sweet spot and have a good idea of how much you need to take to maintain a year-round level of 40 to 60 ng/mL. GrassrootsHealth offers vitamin D testing at a great value through its D*Action study, and has an online vitamin D calculator you can use to estimate your vitamin D3 dosage once you know your current serum level.

Vitamin D Status Is Strongly Correlated With Cancer Risk

A long list of studies has confirmed the correlation between vitamin D status and cancer risk. Here are but a few examples:

• Having a serum vitamin D level of 40 ng/mL has been shown to reduce your risk for cancer by 67 percent, compared to having a level of 20 ng/ml or less.^5,6 Most cancers were found to occur in people with a vitamin D blood level between 10 and 40 ng/mL, and the optimal level for cancer protection was identified as being between 40 and 60 ng/mL

• A 2015 study⁷ found women with vitamin D concentrations of at least 30 ng/mL had a 55 percent lower risk of colorectal cancer than those who had a blood level below 18 ng/mL

• Earlier research,⁸ published in 2005, showed women with vitamin D levels above 60 ng/mL had an 83 percent lower risk of breast cancer than those with levels below 20 ng/mL!

• Similarly, a 2007 study found women over 55 who raised their average serum level to 38 ng/mL lowered their risk of all invasive cancers, including breast cancer, by 77 percent⁹

• Vitamin D also increases your chances of surviving cancer if you do get it,^10,11 and this includes melanoma^12,13 and breast cancer. In the case of the latter, breast cancer patients with high vitamin D levels are twice as likely to survive than those with low levels.¹⁴ Recent research¹⁵ has also found that higher vitamin D levels are associated with a lower risk of severe peripheral neuropathy in cancer patients.

• A new study¹⁶ shows a very clear 80% decrease in breast cancer incidence when serum 25-hydroxy vitamin D levels increase from 20 ng/ml to 60 ng/ml. As one of the world’s most published researchers on cancer and vitamin D, Dr. Garland has maintained for many years that “breast cancer is a vitamin D deficiency disease.”