Yes . Vitamin D is very important for good health. It does affect many of our physiological processes. As shown by the latest research worldwide. Bones, immune system, muscle strength, cancer prevention, thyroid activity,serotonin production, etc the list is very long. Vit D is converted to a hormone in your body, that hormone affect at least 2,000 of your genes, up-regulating some, down-regulating others.
Current governmental recommendations for blood level etc are simply based upon bone health. We need more than that. Humans evolved in East Africa, at a latitude below 30 degrees, in intense sunlight. Our physiology is based upon a constant higher level of vitamin d . About 120 to 140. In the UK , at our latitude of 50+ degrees , much less UVB light is present in sunlight , and we are unable to make Vitamin D , in our skin , between mid -Oct and mid -April because UVB is absent. Mostly our levels are 30 to 60 . Depending upon our lifestyle of course. Most people are indoors, many people avoid sunlight, many people use a suncream which absorbs the light which makes your vitamin D
By increasing your blood level , you will improve your health. As many people have shown here on Mumsnet. There are lots of threads about it ... here are just a few.
www.mumsnet.com/Talk/general_health/2095747-Vitamin-d-deficiency
www.mumsnet.com/Talk/general_health/2376645-Hospital-wouldnt-test-me-for-vitamin-D
www.mumsnet.com/Talk/general_health/2421492-Vitimin-D-can-it-have-this-effect
OP , the amount of vitamin D you require depends upon your weight , and also your sons weight. A 75 kg adult will likely need 3000 to 5000 IU per day to maintain a blood level above 100 .( Preferably in the 120 - 140 range.) If you do that, then great improvements in health may be expected. As shown by the latest medical research. If your son is quite young , he will require less Vit D, because his weight is less. !
I hope this may prove helpful to you.
Best of Luck
BTBH