Vitamin D What Is It Good For? Essential Science-Backed Benefits for Women

Vitamin D is good for three main things: it helps you absorb calcium, it keeps your bones strong and it helps regulate your immune system. It acts more like a hormone than a typical vitamin. It influences over 200 genes, and its receptors are found in nearly every tissue in the body.

Few foods contain much of it, and many women don't get enough sun to make their own, which is why low vitamin D is so common.

What is vitamin D?

Vitamin D is a fat-soluble nutrient that comes in two main forms: D2 (ergocalciferol) and D3 (cholecalciferol). Technically it works as a secosteroid hormone. Most people make most of their vitamin D in the skin when it's exposed to ultraviolet B (UVB) light from the sun. Whether you make it or eat it, your body converts it twice, first in the liver and then in the kidneys, into its active form, calcitriol.

How much you have depends on where you live, your skin color, your age and your diet. Because so few foods contain much vitamin D, many health professionals recommend a supplement (see our vitamin D supplements guide). It's one of the most common nutrient deficiencies in women.

Vitamin D and bone health

This is the best-established benefit. Without enough vitamin D, you absorb only about 10% to 15% of the calcium in your diet. With enough, that rises to 30% to 40%. That matters for women, especially approaching menopause, when the risk of bone loss rises.

If vitamin D stays low, your body may pull calcium out of your bones to keep blood levels steady, and over time bones can become weak or brittle. That's why vitamin D is often paired with vitamin K2 and magnesium, which help direct calcium into bone rather than soft tissue.

Vitamin D and the immune system

In a 2011 review in the Journal of Investigative Medicine, Aranow and colleagues noted that vitamin D receptors are found on nearly all immune cells, and that deficiency is associated with more infections and autoimmune conditions.

Acting on B cells, T cells and antigen-presenting cells, vitamin D may help you fight infection without the immune system overreacting. Other nutrients, including vitamin C, play a part too; our article on multivitamins and immune function covers how they work together.

What causes vitamin D deficiency?

Low vitamin D is very common. Forrest & Stuhldreher reported in Nutrition Research in 2011 that about 41.6% of US adults are deficient (below 20 ng/mL). The main reasons:

• Little sun: indoor lifestyles and sunscreen, which you need to protect your skin, both reduce how much you make.
• Latitude: far from the equator, the winter sun is too low for your skin to make vitamin D.
• Skin color: more melanin filters UVB, so darker skin needs longer in the sun to make the same amount.
• Age: skin makes less vitamin D as you get older.

Signs of low vitamin D range from mild fatigue and muscle weakness to bone pain. Our article on the signs of vitamin D deficiency goes through them. Other gaps are common too: in a 2009 review in the American Journal of Clinical Nutrition, Allen and colleagues estimated that B12 deficiency affects about 6% of adults under 60 and nearly 20% of those over 60, with vegans at far higher risk.

Vitamin D and mood

Vitamin D receptors are found in parts of the brain involved in depression and executive function. Some studies suggest vitamin D helps regulate the conversion of tryptophan into serotonin. More research is needed, but keeping healthy levels is often seen as supportive for mood, especially in the darker months.

How to get enough vitamin D

Fatty fish such as salmon and mackerel and fortified dairy provide some vitamin D, but most women struggle to get enough from food. Sun exposure of 10 to 20 minutes a day on the arms and legs is often cited as a baseline, though it varies a lot with the factors above.

If you take a supplement, many nutrition professionals prefer D3 over D2, because D3 raises and maintains blood levels more effectively. Vitamin D also works alongside other nutrients: vitamin C supports antioxidant defenses and B vitamins help with cellular energy. Our guide to women's multivitamins explains how they fit together.

Where Go Wise Multivitamin fits

Go Wise Multivitamin is a powder stick you pour onto your tongue, with no water needed and a natural berry flavor. Each stick has vitamins A, C, D3, E, B6 and B12, niacin, pantothenic acid, biotin, folic acid, zinc and chromium, plus elderberry extract and kelp as a natural source of iodine. It's vegan, gluten-free and has no artificial colors or flavors. Every batch is third-party tested by Eurofins for heavy metals and microbial contamination, and it is made in a GMP-certified facility.

If you think you might be low, ask your healthcare provider for a 25-hydroxy vitamin D blood test before you choose a dose.

Frequently asked questions

How do I know if I have a vitamin D deficiency?

Symptoms can be subtle, but often include getting sick often, ongoing fatigue, bone or back pain and muscle weakness. The only way to confirm it is a 25-hydroxy vitamin D blood test ordered by your healthcare provider.

What is the best time of day to take vitamin D vitamins?

Vitamin D is fat soluble, so it's best absorbed with a meal that contains some fat. Many people take it with breakfast or lunch.

Can I get enough vitamin D from food alone?

It's very hard. Few foods are naturally rich in vitamin D. Fatty fish and egg yolks contain some, but most people rely on a mix of sunlight and supplements to reach healthy levels.

What is the difference between vitamin D2 and D3?

Vitamin D2 (ergocalciferol) usually comes from plants. Vitamin D3 (cholecalciferol) is the form your skin makes in sunlight. Research suggests D3 is better at raising and sustaining blood levels.

How much sun exposure is needed for vitamin D synthesis?

General advice is 10 to 30 minutes of midday sun several times a week. This varies with skin type, where you live and how much skin is exposed. Sunscreen and window glass both block the UVB rays you need.

Why is vitamin D often paired with vitamin K2?

Vitamin D helps you absorb calcium, and vitamin K2 helps make sure that calcium ends up in bones and teeth rather than in arteries or soft tissue. Together they support heart and bone health.

Related reading: our complete guide to women's multivitamins.

References

• Aranow et al. Journal of Investigative Medicine. 2011.
• Forrest & Stuhldreher. Nutrition Research. 2011.
• Allen et al. American Journal of Clinical Nutrition. 2009.

This article is for general information and isn't medical advice. Talk to your healthcare provider before starting a supplement, especially if you are pregnant, nursing or taking other medication.