Here is why you need enough vitamin D

Vitamin D helps regulate the immune response by modulating the activity of various immune cells, reducing inflammation as well as protecting against pathogens and free radicals.
Ivan Philip Baguma, a nutritionist, says while all the vitamins are essential in boosting the immune system, Vitamin D has a lot to do with immunity.
Nearly four percent of the world's population is affected by one of more than 80 different autoimmune diseases and the majority of them affect women. An autoimmune disease is a condition in which the body’s immune system malfunctions and begins attacking healthy tissue, causing inflammation and damage to affected tissues. 
Studies have shown that people with autoimmune diseases such as multiple sclerosis, rheumatoid arthritis, and type 1 diabetes often have low levels of vitamin D.
Bone health
Vitamin D plays an important role in bone health and immune health and when one has a deficiency, it increases their risk of lupus, an autoimmune disease that affects the joints, skin, brain, lungs, kidneys, and blood vessels.
“Rheumatoid arthritis, a condition caused by inflammation that leads to tissue damage in the joints is common among people with vitamin D deficiency. The deficiency worsens symptoms of the disease among the patients who already have it,” Baguma says.
According to a 2016 review from Clinical and Experimental Rheumatology, approximately 55 percent of RA patients are deficient in vitamin D. Therefore, an increase in the intake of vitamin D-rich foods can help alleviate the symptoms caused by rheumatoid arthritis because the vitamin is essential in bone health. 
In a 2017 Neurology and Therapy review, lower vitamin D levels were found to be strongly associated with multiple sclerosis, a disease in which the immune system eats away at the protective covering of nerves which causes disruption in communication between the brain and the body.
Multiple sclerosis causes symptoms such as vision loss, pain, fatigue and impaired coordination. The deficiency of the vitamin may also aggravate its severity in those living with the condition.
Adequate levels of vitamin D can help modulate blood sugar and promote healthy insulin levels. This could explain why diabetes has also been linked to vitamin D deficiency. 
Risk factors
Research shows that women are more likely to develop autoimmune diseases than men, and also tend to have lower levels of vitamin D. This suggests that there may be a link between sex hormones and vitamin D metabolism, which could influence the development and progression of autoimmune diseases.
Interestingly, 85 percent of women with polycystic ovary syndrome (PCOS) have vitamin D deficiency as well. Additionally, maintaining vitamin D sufficiency can help reduce breast cancer risk by 50 percent. Given all these factors, it is especially important for women to sustain truly optimum vitamin D levels.
How to attain the right amount
According to Ivan Philip Baguma, a nutritionist, you can attain vitamin D sufficiency through a combination of dietary sources, supplements, and sunlight exposure. Here are some ways to increase your vitamin D levels:
Sun exposure: Your body can produce Vitamin D when exposed to sunlight. Try to get 10-30 minutes of sun exposure every day during peak hours (10am to 3pm) while being mindful of the dangers of prolonged exposure to UV rays.
Diet: Include foods high in vitamin D in your diet, such as fatty fish, egg yolks, liver, mushrooms, spirulina and others. 
Supplements: If you are unable to get enough vitamin D through your diet or sun exposure, taking a vitamin D supplement can be helpful. Baguma says it is best to consult a healthcare professional before you start taking any supplements.
Remember, achieving vitamin D sufficiency requires incorporating healthy habits into your lifestyle and following proper medical advice.