Seems to be a decent product and while I haven't been able to gauge noticeable results yet, my main concern is to avoid deficiency for this vitamin. I haven't been tested since I began taking the product and am interested in how subsequent tests will read although the tests available including for this vitamin may not be definitive, but are better than nothing. Living in north Florida I try to get moderate sun exposure here but this product appears to be a good backup especially during times that limit exposure (rain/heavy clouds/Cold) and with aging which most reports available say reduce our ability to take up vitamin D through the skin