For many years, in winter, I take 600 IU of vitamin D3 every day. In mid-November, I will purchase my "winter supply." I will start supplementing when there is little sunshine (usually starting in December) and continue until around March.
Why this regimen?
600 IU is the recommended daily allowance (RDA) by the Institute of Medicine, suitable for adults of my age. I choose vitamin D3 because research shows it is more effective than D2. Moreover, I do this in winter because that is when there is less UVB light, especially when you live at the 37th parallel north. UVB light triggers the body's natural production of vitamin D.
Is it reasonable enough? Yes, until you delve into the science behind supplements.
This year, I did more digging into vitamin D supplements, and it no longer sounds like a good idea. Unless you have specific conditions (consult your doctor for personal medical advice), you may not need it either. Here’s why.
Why Vitamin D is Needed
There are two main reasons:
- Musculoskeletal health (especially bone health)
- “Non-bone” benefits
Starting with bones, you need vitamin D to maintain healthy levels of calcium and phosphate. Through this, vitamin D regulates bone mineralization.
In children, low levels can lead to rickets. The bones of children become too soft, making them more prone to bending and breaking. In adults, extreme vitamin D deficiency can lead to osteomalacia - or literally translated: "soft bones."
However, vitamin D goes beyond bone health. It regulates immunity, affects cell growth and programmed cell death (apoptosis, which is important for clearing cancer cells), and is associated with a range of health conditions. Researchers have observed that people with low vitamin D have higher blood sugar levels. Poor vitamin D status is also linked to heart disease and dementia.
Less vitamin D - bad; more vitamin D - good?
This argument has a major flaw. Let's take heart health as an example: